Container tabs are great for shit you log into, because they're like having a bunch of different, isolated browsers. For example, even if there was a YouTube embed here (which I haven't seen on Lemmy yet) it wouldn't be able to correlate those views to my account because I'm logged in in a different tab, from the way Google sees it it could be anyone on my network. Incognito is similar to that in that you grab a new browser every time and discard it whenever you close the last tab. It's great for transactional stuff, but a little inconvenient for stuff you want to keep logged into, which is where container tabs are great.

And yeah, there are some hella strong fingerprinting techniques, but no one is reimplementing any of those for advertising reasons. They just pull in a script from an ad company, which gets promptly blocked by uBlock Origin. If you use Tor and want to do some stuff that you really need to hide your identity for, you might run into some more advanced attempts to track you.