My first inclination is that embedded ads happen because individual creators are having difficulty wrestling the algorithm to funnel enough views and subscribers their way and because not enough of the Premium subscription fee goes to creators.
This isn't always true as there are a few giants that do embedded ads too, but most of the sponsor reads I see on YouTube are from smaller or more niche channels.
I’ve gotten the impression that for some creators, part of the reason is how easy it is to be demonetised on YouTube. The monetisation filter has become sensitive and puritanical that people even self-censor confronting words now, like “murder”, or “rape”, or “suicide”… I don’t know what TV news or current events shows are like today, but from what I remember watching when I was younger, I doubt any of that would be monetisable on YouTube today.
This isn't always true as there are a few giants that do embedded ads too, but most of the sponsor reads I see on YouTube are from smaller or more niche channels.