Lots of software publishers, telecommunication companies, and other businesses offer bundles, not because of managing physical goods, but because it provides an incentive for the consumer to buy more stuff without adding a whole lot to their production or distribution costs.
Would EA/Bioware benefit from offering a GOTY upgrade for the same reason that they offer the GOTY edition at all? Maybe, maybe not.
Non-existing consumers require more effort as a general rule for any product, so the entire GOTY is just a big marketing push towards them. It reminds them that DAI won a whole bunch of awards and gives them a discount for the game+DLC, because many late adopters might not even buy the DLC at all if the bundle wasn't offered. Us existing customers, as a general trend in any industry, are much more likely to buy the DLC at full price and require much less effort to appeal to.
So, out of the people who bought the game early but not the DLC, who is the bigger factor? Those who will not buy the DLC at full price and will move on if a discount doesn't come soon? Or those who will buy the DLC at full price, but haven't gotten around to it? We can only answer with speculation. You might think it's the former, but EA seems to think the latter. I think it's a tough call, but I'd also think it's the former. Maybe EA has some predictive forecast modelling software that backs their answer up. Or maybe they're wingin' it.
As a general rule, companies tend to appeal to new customers, but they're less "cost-effective" as businesses need more marketing to get to them than they do with their current customers. But it's a trend. Short-term oriented business, as usual. So they choose to neglect "current customers", betting that they can make more profit off of them.
It's really obvious with IAP and phone carriers, at least in my country: they perpetually give good offers to new customers, while their tech support usually sucks...
Once again, EA does decide the prices. But customers can say they feel these are too high given the current situation.
And from a business standpoint, I'm not sure they're making the best decisions: I don't think their marketing team see all the parameters, and they may not be thinking enough "out of the box". Origin, and their store, is not going to lead by applying the same old practices and lagging behind others...
But that's my opinion, and I'm certainly no marketing genius.