So Jon Bon Jovi is richer than Metallica but has sold less albums?

I can't for the life of me remember, but I read a list yesterday of the world's 25 richest musicians, and it was from a very reputable source, I think it was Forbes? it said that U2 was the richest, then Bon Jovi, then AC/DC or something like that. It had justin bieber and Rhianna in there, too. But apparently Metallica was not even included, despite the fact that they have sold 200million albums worldwide, as opposed to Bon Jovi's 120 million. As far as I know Metallica also plays huge arenas incredibly often so Why are they not even in the top 25th spot? I have a feeling that the media is extremely buyist even in this information. What do you guys think?