One of the biggest indirect causes of ageism I've seen is the traditional career path forced many engineers out of engineering - there is/was an attitude at places like IBM of: "If you want to make bank, you need to go into management or sales". Years later, an engineering crunch makes engineering into "where the money is", but you largely lost a generation of technical experience that took a break of a decade or two.

My father got lucky in that he was successful in his transition out of engineering, and was 67 by the time his position went extinct, but there are a whole bunch of folks who would rather have been engineers than otherwise, but ended up missing out on a couple decades where the daily tasks of building software changed dramatically so gained less in technical expertise than they should have, and were left hanging around age 50.

I have a ton of cultural criticisms of the current tech industry, but the one thing that it is absolutely getting right is valuing creation. The damage that could have been caused by the Google/Apple cartel has been limited largely by the startup industry that, for all its faults, has as a crucial belief that the act of building things is valuable, and that people who make things are the ones who create the most value.