One of the reasons might be that Metallica's songs are simpler than Maiden's, and thus easier to digest. To me it took a long time to get into Maiden properly, and I've heard from many others that it still takes several listens before one can "comprehend" a new Maiden song. And a lot of people don't have that patience, so if they're at all into metal, they will choose Metallica. (I'm not saying Metallica songs are bad, just that they aren't as complex.) Metallica made themselves quite well-known with the Black Album, have been able to keep themselves known, and the phenomenon has been feeding itself so new listeners add up all the time. Also, I guess they have just been lucky.So... this is a genuine question:
Why are Metallica the biggest metal band in the world right now?
By the way, I spent the beginning of the 90s devoutly listening to Metallica, too.