What advertisers need is more readers, more potential customers for their services.
I agree with the latter but not with the former. Nowadays a new cryptocurrency exchange, to give an example, is going to get a lot more customers if it advertises on a Youtuber with millions of followers than by advertising on the forum.
Raising the quality of forum posts will not change that.
Earlier, new projects were conditioned to have their ANN on the Bitcointalk forum if they wanted to be listed on CMC. It wasn't a bad idea at all, because that way they were forced to have an open channel of communication. It also had a significant impact on the increase in forum activity.
I think that changed sometime around the time when Binance took over CMC, they probably didn't want to contribute to the development of another authority.