I get what you mean; the letters themselves don't necessarily further marginalize anyone. But as an ace person, I've experienced mockery and discrimination from inside the LGBT community (meaning those letters specifically, hence the omission of the +), people claiming this orientation isn't real and what have you. So to me and, I would argue, a lot of other ace (and aromantic, I might add) folks I know, the omission of the I and in this case A feel like they further perpetuate this mockery inside the community. It's a context thing, really. I'm glad there's at least the +, but it doesn't really help what I experienced from people who should know better than to enforce the same excluding narratives we know from cishetero people.
Just food for thought then, perhaps. I'm not running around demanding everyone caters to my needs specifically, but it would be nice if people gave thought to this issue once in a while.
Then again, I guess we would need to include the P as well, so... yeah. Maybe Tapas went for a compromise there, since Q for Queer and Questioning includes quite a bunch of people already.