[tentacleuno]

> I am simply puzzled by how much modern app development actually revolves around the use of third party APIs

A staggering amount of web development relies on third-party libraries: React, Vue, etc. etc. It's just the way things work. You can make a website without the use of external resources, but it will be a little harder if you're building something more complex (with various states, etc.)

> Is modern app development all about putting independently provided pieces together ?

I would argue yes, the majority of development is putting pieces together and getting an output. They could be third-party, part of the standard library, or something in between :)