This. And it isn't just scrolling. Ads typically come from some ad server somewhere, often not the site you're trying to read. You get performance hits (particularly on slow networks). Moreover, if you're trying to view a site that was crafted for desktops/laptops on a smaller screen (e.g., a tablet or a phone), ads can be so intrusive as to really mess up the coherence of the page. (And yes, many sites have "mobile" sites for tablet/phone users, but often the tradeoff there is that you get a far less comprehensive site.]
Then too, many sites are designed to be glitzy, just assuming that the reader has the processing power to handle the glitz. Many of us do... but many do not. I notice significant differences in site performance when I'm traveling (typically hotel wifi, 12-year-old laptop) vs. when I'm at home (fiber optic WAN, high-speed mesh LAN network, 1-year-old Apple Mac Mini with an M1 processor). It's clear that a lot of site designers have pretty much abandoned any effort to support those with less processing power or network speed.
Advertising on web sites doesn't have to be a major problem, but that's a function of intelligent web site design. Like everything else, high-quality web site design costs more than "meh" design; too many journalism sites seem to opt for "meh," rather than make the extra investment to produce an intelligent site.