Sports boards, specific interest boards, eccentric little boards, and anything not tied to a major Yahoo service (like Finance which is saving stock boards) are gone or going by March 1. This seems like a mistake and certainly harms the experience for long term users. No way to monetize? That seems to be the issue but it may be said of email as well.
The finance boards get targeted advertising because the advertisers are to stupid to realize that most of the users here are either timewasters with multiple ID's talking to themselves, serial scammers or political posters.
I suspect these other boards bring absolutely nothing to Yahoo.