It is not exclusively about the ammo, it's the combination of infinite ammo and the extreme versatility mentioned at the beginning of my comment. Of course you can use other weapons, but you don't really get a reason to because it is enough for every situation.

I don't understand the "you issue" thing when the statistics image linked here shows that the Beowulf was the most used weapon across all players. That's like, the most objective, empirical proof possible that it is not a "me issue"!