When I forget to sign in to YouTube, I see the same pattern, shitty ads that are clearly only allowed because otherwise YouTube wouldn't have sufficient ad inventory to meet their internal KPIs.
I'm not fully sure about this, an ad network which does that very reliably can probably charge the ad provisioning companies extra due to it being on more high quality sides/locations and pay out extra little due to having "high quality low disturbing" ads.
But with the Google being a quasi monopoly for ad networks on any open platform and most people either blocking all adds or no adds there is just little room for alternatives. I do use uBlock Origin for some custom filters, but I which instead of "on" / "of" there where "on but more like privacy badger" / "on full" / "off" with the first being the default so that users can create an insensitive for better ad handling.