I imagine TV before I was born was a little more like this since you could't just buy generic ad space - you needed to deal with the producers of a show specifically to get into their ad slots - but for TV when I was growing up, ads were ads. They'd target your age group (ads for kids toys during breakfast cartoons), but it just never occurred to me that anyone would think it was an endorsement of anything.
This is such a confusing concept to me. Do people really think like that? I know they do now, because it's a self-reinforcing concept. Yelling loudly that ads are an endorsement of content makes it true - since if you're an advertiser and you know that attitude is out there, and you still run an ad, that's now a conscious decision and everybody knows it. But it seems like this came about artificially, via activism, rather than people naturally making the link that ads imply endorsement.
That's different on YouTube, where the content is much more heterogeneous, where you have super-optimized, ad-friendly influencers with millions of subs who take great care not to offend (and are therefore great to throw ads at) next to fringe political ideas and people with mental health issues presenting their world view.
I believe funding is often considered as an endorsement, and ads are the primary source of funding for most media companies. Similarly, you'll often see disclaimers on Twitter "retweet != endorsement" because people tend to understand it as such.
I believe that the bigger deal is subconscious association. I have no idea whether it's true, but putting McDonald's ads next to a documentary on factory farming seems unwise.
I had expected the younger generations to be "digital natives", but they're not. They know their apps and services, but it's not a generalized understanding to how things work or what's common. Imho the fact that adblocker-usage isn't approaching 100% is a powerful demonstration of it.
Additionally, there's the subconscious effects. Even if they consciously understand that it's based on their ad profile, brand will likely still not advertise there. There may be some exceptions (Benetton comes to mind), but I don't think Disney ever wants their ads to be displayed in an article about Auschwitz.