I'd expect people, DJs or not, to say they didn't like a film if they didn't. It doesn't mean they need to get a life, they just hold different opinions from other people.
As to why - well, critics (and DJs) may have seen dozens of biopics about musicians and think this isn't as good as others. Whereas Queen fans may only have seen this one and have nothing to compare it with.
Or whatever. I won't be seeing it because I was never a huge Queen fan anyway. Nothing to do with the teeth, though.