If these sites just go for some verification before promoting these scams, it would be very good for the visitors. Verification can include Mobile verification, Identity verification etc. These sites are an open image of crypto, if these sites just reduce their earned money by a bit and plan for long term then it would be beneficial for all of us.
I'm not defending Coinmarketcap, but they are a stable site with stable income from their advertising if they know that a project is a scam they are not going to accept, they are an advertising company and not a review and rating site to tell us what are scams and what is not, the burden is on the investors, not all that glitters are gold, investors must do extensive research and not rely on advertising company.
I agree with your point that the coinmarketcap site is the biggest site in the advertising industry and I personally think that they are one of the most trusted sites because they display complete data including crypto price charts. Apart from that, not just any coin can be registered there, only good coins can be registered there and if there is manipulation of coins, I don't think they will last long.