It is because "the community" decided they should be kept.  It was voted on democratically, after all.  Are you suggesting that democracy is an unrepentable evil?  Fascist!

Since troll metal is a description, not an actual subgenre, bands of internet trolls are allowed since they fit the description of "troll metal".  If a band can be called "troll metal", then they belong under the umbrella of troll metal.  Understand now?

It takes maturity to understand that sometimes, some things are true simply because most people believe them.  If you feel otherwise you have maturity issues you need to deal with before contributing to this democratic, open-for-all encyclopedia.