Take FB as an example. FB have 60k employees, 12X the 2012 IPO number. It also costs 12X to run facebook today. They don't do that much more today than in 2012. They mostly just do things a more complicated way.
IMO, the reason for that is actually revenue. Beyond a point, there's no market discipline reason for mitigating costs. FB is profitable enough with its >30% margins. Investors don't want them to cut the salary bill. They want FB to hire people, invest, do more stuff & grow.
If FB revenues had plateaued around $10bn, I'm pretty sure FB would still exist. FB would have 90% fewer employees and users would not experience much difference.
Once you have all these extra people, and basically the same set of tasks at hand... sluggish ways of doing things and inefficiency are basically guaranteed. If 500 devs are now working on an area that 50 people previously ran, it's going to look like ineffectiveness at the ground level.
A lot of the software industry is like that. Half the industry, like most internal dev orgs are not very capable or motivated, and things look sluggish at ground level. The other half is flooded with cash and great devs, but teams are bigger than actually necessary.