YouTube already has ToS on their API and has paid tiers. But a lot (most?) of the third-party apps and tools bypass the API and directly scrape the site.
I'm sure there's an in-depth reason for it, but there is one that scrapes Old Reddit, instead of the main site, and it works great for me (Stealth on f-droid). There's also RedReader, a client that was allowed to keep API access because of it's accessibility features... which I guess Reddit just couldn't be bothered to implement into their own app.