Youtube likely tolerates it because even with a 60% revenue share going go creators, often half of viewers pay nothing (no ad views or subscription), so sponsored segments can fill the gap for the creators.
Note that Youtube premium does include the ability to skip sponsored segments though.
If content creators can't live off of the ad revenue that YouTube offers, then that is another thing to lump the blame of at the feet of YouTube. They not only turn a blind eye to content creators ruining the service I pay for, YouTube is the one themselves who has created the conditions in which the content creator feels the need to pursue external advertising.
There is obvioulsy enough advertising money in the world to support both YouTube and content creators, because that is exactly what is happening right now: advertisers are paying either YouTube or the content creator directly. For some reason, a lot of content creators can't make it by just working with YouTube, despite there being enough advertiser demand for it. That tells me that YouTube is being stingy.
[0] Which, BTW, many content creators are not properly marking up their videos to allow for the skip feature to work.