Because making more origin stories is going to somehow kill DAI right?
So DAO is the only game capable of giving the player an insight about their PC's background? It's not like we're asking for a DAO2. I just think that a few lines of a super vague text about my PC is not enough to make me care for them. Maybe for those who are all about headcanons prefer it that way, and it's fine, but I don't.
The origins in DAO served a purpose. Here you had a character doing their own thing in their own little world, then something unfortunate happens and they need to get out. Duncan conveniently arrives to pull you out of the mess and recruits you into the Wardens.
What purpose would they serve in DAI? Your task is already set. You're all going to the conclave for one reason or another. The only way you could possibly roleplay is through dialogue and specifically with regards to your relationship with people from your origins as well as your viewpoints regarding the Conclave. All of this is already done in current game via talks to your companions about your own personal views and past as well as how you handle the elements of your background.
It's not even possible for you to roleplay through actions, because you're not supposed to remember what happened for a significant part of the Conclave.
Does DAI come equipped with a memory eraser?
Smile!

Furthermore, the idea that origins are the only way to get insight on your character is pretty counterproductive to roleplaying. If you need to set your character's personality in stone in the first 30 minutes of the game, then there goes any chance of any character development.
DAI actively encourages character development via dialogue and this is shown multiple times in the game.
This can be demonstrated by the simple example of being asked at different points in the story whether or not you believe you're the Herald of Andraste.
Another example is how you handle your faith (or lack thereof) after Haven.
If I recall correctly (and I pretty sure I do), there are next to zero questions about your Warden's character and their development in DAO. Everything you do is headcanon'd and there is no in-game recognition other than approval losses.
In any case, I'm fairly certain the intro sequence has enough RP options and dialogue choices to shape the initial personality of your Inquisitor.
So how about you exercise some development of your own and try to adapt to a system other than Origins yea?