Play in games -- Why aren't they all for the 16 seed?

because it makes too much sense

Because many years there are weak teams that win auto bids in their conference tourney that rank FAR bellow any at large bid.

I think this goes into the AQ for small conference debate.

Here's the article when they revealed the new format. You have to think of it as 8 teams: the last 4 AQ's and the last four at-large, instead of 11 seeds and 12 seeds. I guess they decided 4 teams who would not have been in the 64-team tournament was more fair than the taking half the berths in the "real" tournament from the worst 8 AQ teams.

It's all based on the strength of the AQ conference champs

Because the conference champs of shitty conferences get automatic births in the tournament.

And since those teams are generally ranked pretty low, the low seeds are reserved for those teams.

So the last available spots for teams to get an at-large into the tournament are ranked higher.