I think there are way more companies than you think that give manager-level devs a light enough management load that they are able to (and are expected to) writ

I think there are way more companies than you think that give manager-level devs a light enough management load that they are able to (and are expected to) write extremely high quality code (indeed, some of the highest quality code in the whole company). They are also expected to carefully review code written by their subordinates. When hiring, these people are given coding tests just as a pulse check to make sure they can actually code, since so many manager-level devs have apparently lost that ability. I think there is a disconnect between manager-level devs who expect a glorified project manager position with zero coding requirements (and are thus insulted and shocked and assume it’s ageism when they’re given coding tests they cannot pass) and companies that expect their principals to hack on code until retirement. And while blatant ageism is clearly a problem in the industry, I’d bet that at least some of it stems from this disconnect.