But just last week I watched the hard work of a coworker get completely bowled over by another manager's "congrats on amazing work" email chain to someone else who used the work of my coworker without recognition.
It's hard to imagine a promo system that rewards hard work, where feedback comes from ones peers, and only promotes a fixed number of people where these kind of zero-sum issues don't appear.
SmallCorp you all work for the bottom line or company goes bust. That acts as a damper on empire builders who build for their own sake, though there is still that behavior.
BigCorp it's unlikely your contributions are going to impact much of that kind of thing, even if you're up in senior management. So you're there for your Career(tm) first, company $$ success second. And in fact that is directly promoted through Perf, etc.
So the aggregate behavior of individuals is not only to self-promote but to encourage the self-promotions of others, that's how we get ahead by the measures defined as "getting ahead" by the company: internal promotion, project glory, internal and external speaking engagements and publications about your project, etc.
So a 100 person "congrats" and "that's amazing!" email (or its equivalent on LinkedIn) or whatever is just reasonable professional behavior. You're not a jerk for promoting yourself, you're just doing what is expected of you. The professional behavior of the modest but "plug along and do my job and help out and not self-promote" person is the one that's suspect in this scenario. The company _wants_ you to self-promote.