You don't even have to get close to Google or FB before running into issues with JSON. At a previous job we were working on REST APIs that topped out at around 100qps. Performance wasn't what we wanted and we were initially pointing the finger at Python and the database. We started profiling the application and found that most time was spent in JSON serialisation - which is actually implemented in C. Unless you're serving the browser there's really no excuse for not using a binary format.
The excuse is that there are not enough seasoned software developers, and what used to be a relatively meritocratic discipline is now a shit show.
Problems started somewhere in early '00s when "software architect" became a dirty word, and one hit wonders like Paul Graham pontificated that "young is smarter".
