I feel like many companies are afraid to do this because there's no guarantee their newly trained people will stay for so long as to make it worthwile. What if instead of "literally anyone" they trained non-technical colleagues that have already proven commitment?

Anecdote: next to my Information Science studies, I worked as a community manager for a few years. This was at a small startup so I was in practice doing more than that (marketing, data analysis, QA, etc). Once I finished my studies my CTO asked me to become a developer - he knew I was dedicated to the mission, knew just a little about coding but had the right personality for it. Sadly, in the end they realised that they didn't have enough time to train me and had to withdraw the offer.

I think it would be great if more CTOs made such offers, though in practice it seems unlikely. Small companies are less likely to have the resources to train and in larger companies perhaps the CTO is less likely to know community managers and such well enough to make such offers.