Facebook developers are doing some really great stuff. For some reason it doesn't translate into a really great facebook or instagram. The experience is worse

Facebook developers are doing some really great stuff. For some reason it doesn't translate into a really great facebook or instagram. The experience is worse compared to 10 years ago. If they hired 10,001 of the best developers not working at facebook I think their products would be the same or worse. Is there a single person responsible for the vision?