Basic step in creating any quiz on this site: Enter multiple possible answers. No decent quiz expects you to put "the", and also multiple spellings are accepted, Guns N' Roses, Guns and roses, also last names like Hendrix should be accepted, CCR.
to be fair, the band's name is technically "Eagles" and not "The Eagles", but it's just arguing semantics at that point. both answers should be accepted
It's always been The Beatles, The Rolling Stones and Eagles. So it's not about the consistency of the quiz maker but the band names. However, I agree it shouldn't be about "the".