YouTube I am not so sure, I have a feeling it has to do with how little sway the content owners have in the ads that play on their videos. If you are a big channel you may have enough of an audience that more traditional brands would like to reach but for most I imagine you take what you can get. Though I really am not sure how YouTube does things--they are one of the "walled gardens."
The same commercial 10 times in a row is an awful experience and most media owners try to avoid it, but depending on the content it could be the only ad bidding against you as a viewer. Generally there are frequency limits in place to avoid this from happening. On more mature platforms this tends to be the case. Sometimes it can't be avoided due to glitches, poor ad tech stack integrations, or greed, the owners would rather prioritize the cash over UX.
The same commercial 10 times in a row is an awful experience and most media owners try to avoid it, but depending on the content it could be the only ad bidding against you as a viewer. Generally there are frequency limits in place to avoid this from happening. On more mature platforms this tends to be the case. Sometimes it can't be avoided due to glitches, poor ad tech stack integrations, or greed, the owners would rather prioritize the cash over UX.