Number of employees doesn't scale up with the number of messages hitting queues.
No those acres of employees at Twitter are showing each other powerpoint presentations, ordering lunch for each other, and subdividing again and again tiny slivers of functionality into more and more product management teams, none of whom have sufficient authority to make any material improvement to the product.
I can't you upvote more than one time, unfortunately. I can't speak for Twitter, but this is very true of many companies. As they grow, they start structuring the product development into multiple verticals with specific specializations like "UX design", "graphic design", "user engagement", "backend team", "frontend team", "devops team" and so on, but they fail in creating enough horizontal cross-contamination and the central direction gets weaker and weaker; the teams start to segregate and blame each other (frontend team says that backend team is providing them with bad apis, devops team complain that backend team is using too many different technologies, ux team complain that graphic design hasn't followed their advices, etc.), and many meetings are setup to solve these conflicts, and to implement new processes and new information workflows that are ever more complex (and thus slow) to make sure that everyone is useful. The end result is that product development gets slower and slower; theoretically, the end result should be that releases have superior quality (when you eventually get around making one), but it's hard to justify the differential costs compared to shipping fast and iterating.
No those acres of employees at Twitter are showing each other powerpoint presentations, ordering lunch for each other, and subdividing again and again tiny slivers of functionality into more and more product management teams, none of whom have sufficient authority to make any material improvement to the product.