> Why wouldn't someone jump at an opportunity to prove the thing/service they provide actually works, unless they were unsure about it themselves?
Because advertising in some form certainly works. If you can determine that approach "A" that everybody is doing is actually a waste of money but approach "B" is effective, then you can develop services around approach "B" and market them based on these findings.
Nobody is arguing that advertising doesn't work at all, but my argument (which I think a lot of other people agree with) is that the effectiveness of online advertising (and maybe advertising in general) is overblown.
Because advertising in some form certainly works. If you can determine that approach "A" that everybody is doing is actually a waste of money but approach "B" is effective, then you can develop services around approach "B" and market them based on these findings.