You realize that there is a lot of stuff that goes on behind the scenes, right?
They need to scale their systems, maintain reliability, scale their processes, build internal tools, run experiments, work with 'legacy' code and within the existing architecture, etc.
It's not surprising product development has slowed down. In almost all cases it seems like the speed of product development is asymptotic.
Hiring too many people is still the number one thing that can kill your growing business. The communication costs alone eat a bunch of headcount so if you don't desperately need the people then you shouldn't hire them.
The problem generally starts when you hire a bunch of people without fixing broken processes first, these people then push back against fixing said processes, and the rot sets in.
They need to scale their systems, maintain reliability, scale their processes, build internal tools, run experiments, work with 'legacy' code and within the existing architecture, etc.
It's not surprising product development has slowed down. In almost all cases it seems like the speed of product development is asymptotic.