Well, to answer your question in two words: Mass Effect
That's the short answer.
For the long answer, I'll quote Brent Knowles, lead designer of Dragon Age: Origins
There's a phrase in there that bothers me badly, so I'm going to grasp it firmly in my maw.
It became more difficult over the years to argue for doing anything markedly different from what Mass Effect was doing. It was a project that struck much closer to its schedule, did very well (ratings and sales) and had the wow factor (the Silent Protagonist of DA: Origins never had the appeal that Shepard did, whether in company meetings, publisher proposals, or on press tours).
I find it ironic that Mass Effect 3 so thoroughly demolished all of the above.
There's a lot of influences in DA2 and DAI from Mass Effect 2 and Mass Effect 3, but just as the problems with Mass Effect 3, their problems stem from the fact that BioWare's takeaway from Mass Effect 1 was fundamentally incorrect.
What did people latch on to in ME1? The recycled Generic BioWare Female Starting Party Member and Male Starting Party Member (Voiced By The Same Guy As In The Previous Game, In Fact)? The awkward shooting controls? The sex scenes?
Maybe some people did, sure.
The big thing that made the big fandom was The Sense Of Awesome. The Sense of Scale.
The oft-maligned MAKO missions had a lot to contribute - you'd notice that DAO has a lot of epic open spaces, and an overall feeling that you're on a large-scale, if sometimes dull, trek through a whole damn country. It's a palpable sensation that DA2 lost partly because of the recycled maps and partly because of the godawful pacing (also because Kirkwall didn't feel like a story hub, but like a Prologue City #2 right before the actual plot starts and dumps you into the actual sandbox -> sort of like Haven is in DAI, you know?).
DAI reclaims some of that scale with the huge locations, but they're still painfully unconnected, y'know?
Mass Effect had problems with pacing, too, but in general, there was a pervasive connectitude. Departing the Normandy on a planet? You gotta go to the airlock and wait for it to cycle. You gotta ride that gorram elevator from the spaceport, or take a cab.
Going down on a planet ("Haha, Beavis, he said 'going down'!"), you get an animation of the MAKO getting dumped onto it, you don't magically teleport down.
Mass Effect 2 lost a huge chunk of that. It's obvious the cutscene loading screens with the schematicky arrows were supposed to replace all that to show you the transitions, but after Mass Effect 1's 1980s Decompressed TV Series style of narrative, Mass Effect 2 feels like a stage play adaptation of the lost episodes of that series.
"We can't have nudity, so here's more swearing. We have more budget, but still not too much, so we'll magically jump from set to set and hope the audience can follow along. We couldn't get half the cast to come back, so here's some more files from the Standard BioWare Cast", etc.
Dragon Age 2 felt similar - you're moving from an epic sprawling multi-movie series into a low-budget TV Series whose writer had lots of ambitions but the cast didn't play along and he had to edit it from what little footage he could force them to make.
Mass Effect 3 tried to get some of that back, but... they still didn't understand what magic element they lost, and so they tried to build up from the elements that made Mass Effect 2 a smash hit - which was accessibility to non-RPG players, diverse, if cliche, characters, and a linear plot. Sure, ME1 wasn't the most non-linear of games, I admit, but the order you did the planets in mattered A LOT (again, I regret that the subsequent games didn't do anything with "Garrus who wasn't tempered by Shepard before becoming Space Batman and is therefore Space Moon Knight" or "Liara who had lost her marbles from starvation" because ME3 ignores even what little character-movement these characters had in ME2 in favour of the brightest option available).
Mass Effect 3, in short, tried very hard to pretend it didn't have two 60-hours-worth-of-gameplay games behind it because it had to sell on platforms which didn't have those available, which actually tripped up Mass Effect 2 already (another past mistake nobody learned from).
DAI, like Mass Effect 3, had the same problem with viewer retention: it wasn't actually aimed at the long-time fans.
We can engage in pointless sophistry all day long, but for the most part, "it's a perfect jumping on point" were actual words said by a BioWare person to promote a threequel before, weren't they?
DAI doesn't resolve hanging plot threads from the previous games (a lot of folks fear The Architect's story will get resolved in a paid DLC, and he will be un-killed like Leliana and Corypheus were), doesn't retain design decisions from previous games (I'm pretty sure Halo players can recall similar frustrations when control layouts were changed from game to game), doesn't even try to offer things that you'd expect would be carried over from the all-so-important Mass Effect.
It's like after Dragon Age 2 crashed and burned mostly due to a mismanaged development process (most likely due to the budget concerns), they decided EVERYTHING that was learned from it would be restricted to "Varric is popular" and "everything Hawke touches, dies". You know, not the interface evolution (like them or hate them, the emoticons were an IMPROVEMENT with the stupid "guess what this dialogue option will actually do" game and it was dumb that neither ME3 nor DAI retained them), not the importance of internal party romance (as confirmed by ME3, yay), and certainly not the "PC gamers need a PC-friendly control scheme and console gamers need a gamepad-friendly control scheme and it PAYS TO ACTUALLY TEST THEM FIRST" fiasco.
And what do we get as the outcome? Half the (constructive) complaints against DAI were the same as against ME3 and DA2.
"Auto-attack is borked", "why did you change the controls", "the ending comes out of the left field", "did anyone actually playtest this", "why does the face look different ingame than in the CC", "plot flags didn't import", "was THAT what the dialogue option meant", "enemies are level-matched badly", "filler filler filler", "party doesn't obey "hold" command at all", "no dwarves are romanceable?!", etc.
I mean, isn't the point of feedback to learn from it? Or did the torching of the old BSN also involve removing all obligations to learn from past mistakes and improving upon the experience gained from making them?