Sure, but if the only ad restriction was mandatory blocking of third party content, you'd just see ad agencies work out ways they can get the content they want to serve hosted locally (and lots of more interesting third party embedded content cease to exist due to it not having the same commercial rationale for workarounds...). If you start forcing companies not to promote third party products with anything that even looks like an ad, you'll just see a greater proportion of the free-to-access internet turn into paid-for reviews and influencer marketing. Not sure that'd be an improvement, and I'm pretty sure the next logical step of getting the content cops ruling which content looks too commercially-oriented for us proles to look at is even worse.

You can block third party advertising structurally using uBlock without ruining the internet for everyone else.