> If these people were happy to be L5 for the rest of their life and not want a promotion, companies would be happy to employ them at that and have them lead Software projects.
I'm not sure if that's true; many companies have explicit "up or out" policies, and some don't codify it that way, but don't particularly want their employees to find their happy place and stay there.
Not really. Google for example will let you stay at L5 (and now even L4) for your whole life. In fact there are tons of such people who have been at Google for say 10+ years and are L5.
(It's a different matter now that you can be laid off. But you won't be dinged for being a well-performing L5).
Google is an extreme outlier as far as employers go. What Google does only has bearing on the employment experience of most of the people here, and software engineers in general, in terms of companies trying to emulate Google by building runways out of bamboo.
Can you name any major company where an L5 equivalent level is not terminal? Many people stay ICT4 at Apple for a long time.
Performing well at a level is not directly related to promotion. You are expected to perform well as ICT4 or L5 (i.e. get good ratings), but promotion is an orthogonal process.
