[lucozade]

Who said they died because of their belief in the Resurrection?

I think it is highly likely that His followers believed strongly that He was the Messiah and His message had divine provenance.

It's much less clear which parts of, what became, the accepted view they considered worth dying for.

Maybe they believed in the truth of the Resurrection. Maybe they weren't aware of the claims (ok that's unlikely). Maybe they were aware and decided that it was good for the message (much more believable). Maybe they thought that it wasn't that important to the overall mission either way.

I don't know the answer, of course, but it's perfectly plausible that they didn't believe in the Resurrection and still fulfilled their mission. Plenty of people have died for what they believe is right without needing to have a mentor rise from the dead.