We were saved by the bell when they announced the increased account limit for S3 buckets (1M buckets, now, 1k I think before).

Just before they announced that I was working on creating org accounts specifically to contain S3 buckets and then permitting the primary app to use those accounts just for their bucket allocation.

AWS themselves recommend an account per developer, IIRC.

It's as you say, some policy or limitation might require lots of accounts and lots of accounts can be pretty challenging to manage.