Bots or not, Facebook has orders of magnitude more traffic.

HTTP traffic is different from run this CPU intensive pipeline service for 10 minutes and now increase the volume by 100x in a few months.

I used to manage a popular app/website that had tens of billions of real user page views per month. It wasn't easy but it also wasn't hard. It was surprisingly easy with a single large Postgres DB, a lot of caching, optimized tables and queries.

Yes, but their shapes are very different. Most users interact with a small, geographically constrained bubble. It is (comparably) an easier problem for the usage patterns of Facebook.

The app is also designed so when you open Insta, only a few images are shown, infinite scroll is there for a reason. The search page suggestions? Probably from a cache and then re-ranked quickly.