That very subjectivity drives the discussion which dominates the airwaves if you think about it. More guys can win when you say it is most "valuable" rather than "outstanding"
If it's just best player then Shaq, Duncan, LeBron, MJ win like 80% of the MVP's over the last 25 years and there isn't a ton to talk about. People like us wouldn't have threads like this. So that is a big reason they keep it that way IMO.
But with "valuable" you can give it to guys like Barkley, Malone, Iverson, Nash, D Rose. Getting that award helps those guys a lot in terms of reputation.
NFL kinda same thing. As good as a year as Matt Ryan had, if the award was most outstanding then giving it to him over Aaron Rodgers just kinda is a stretch. Matt Ryan needs MVP more than Aaron Rodgers. Almost like a UFC/boxer needs the belt more than another guy to establish himself as legit.
So then more guys win MVP which creates more marketable stars which is generally good for the leagues.