As Criticyl said, the server is premium, so cracked accounts can't join.
Maybe Minehut could add a feature like that in the future to allow unregistered accounts.
A minecraft account is only $26, though (which is a bargain compared to other games imo). Most servers don't allow unregistered accounts because it can cause chaos when using commands. An unregistered player can use any name they want, even if it is taken.