I tend to be an advocate for including more rather than less, but one argument for requiring a baseline level of notability is that sufficiently obscure topics are difficult to verify information about as well as making it unlikely that people will notice, and Wikipedia gives additional credibility to whatever's currently written there (whether it should or not, it does).

Less obscure topics are both easier to verify and more likely to have someone looking at them and going "wait, what, that's not right...".