Reasons why being able to put a theme on your OS is necessary for it to be accessible

Different people have different accessibility needs; it is impossible to make a single theme that everyone can use

Some accessibility needs are incompatible with others, so having only one or even two "accessibility" modes can't cut it (e.g. dark + high-contrast theme)

The "accessibility" themes are the least tested and most buggy ones; so preventing users from adding themes means we're stuck with the bugs

0

If you have a fediverse account, you can quote this note from your own instance. Search https://scholar.social/users/researchfairy/statuses/114219039124623316 on your instance and quote it. (Note that quoting is not supported in Mastodon.)