You have to realize that a company is always optimizing for efficiency and salaries are no different.
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.
There isn't a single optimization. Define efficiency. Define over what time frame.
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
Why are people so determined to just shill for companies? Do you know how many people are unemployed for Christmas today, while you're out here tasting shoe leather for these organizations with more money than God?
They're not going to take pity on you, you know, no matter how much you grovel and beg.
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.