e.g. googlevideo.com resolves to 172.217.4.196 and the PTR for that IP is lga15s48-in-f196.1e100.net
They even have a faq for this: https://support.google.com/faqs/answer/174717?hl=en
Most sites I visit these days--even super common sites like medium.com--have dozens (or even the hundreds alluded to above) of dependencies from seemingly unrelated sites. I have no idea if those are CDNs for common js libs, analytics libs, spammer libs, tracking libs, or what. I recognize things like CDN links for jQuery, Bootstrap, React, etc. I see many that seem to be Facebook tracking.
Of course, blocking many of these breaks the page. I have started to avoid sites that break without access to urls I can't identify. But this is both laborious to vet, and isolating.
There is no longer such a thing as easy, anonymous, inclusive web browsing.
DNS has been made hierarchic for this reason.