>I don't understand why engineers who don't want to be managers give a shit about corporate promotions or corporate ladders.

HR/MBA types value titles, buzzwords and other nonsense because most of them are incapable of actually parsing a technical resume. So, if you're going to look for a job, filling in your title as "developer" over a period of multiple years is a losing strategy.

By the same accord, without titles, buzzwords, etc as an engineer I won't be able to differentiate between resumes of a regular graduate level physics educator and one who is capable of nobel prize level research.