Giving out promotions when people are already working at the level they'd be promoted to is simply a waste of money.
This is the author's biggest mistake. If you voluntarily work on tasks above your pay grade you are signaling to the company that you don't need a promotion.
The problem the OP faced is that YouTube is optimizing under a short time frame and under the belief that employees are fungible. The latter being a common problem with big orgs, thinking there is no value to institutional knowledge. Yet in reality that is often extremely important
Must be “efficiency” why my coworkers have constant coffee breaks to talk about kids/sport/travel while MRs are open without comments for weeks.
They're not going to take pity on you, you know, no matter how much you grovel and beg.