I think the issue with these massive scale apps is that people want better and fresher features which are not always well defined and get lost in the maze of product development of a huge company. They have to make decisions, do we go with web3 stuff or do we improve current NLP system etc etc. Making decisions is much easier for a small startup than a behemoth of twitters size. And yes, it takes many people. 1000 engineers? Maybe not, bloat has set in at that point, but a few hundred for sure.