Honestly I think Uber switching was more of a business decision as their employees had trouble figuring out how to properly use Postgres. Instagram definitely has different data needs, but is probably much bigger than Uber wrt data. They use Postgres successfully via Django no less!
As someone who participated in this transition, I don't think that was a part of it. The new database layer took quite a bit of instruction to use properly as well, and there were plenty of people misusing it.
https://engineering.instagram.com/sharding-ids-at-instagram-...