The main reason IMO is spending time on a JB update only costs them money, and HTC isn't in a position right now to be spending money on things that don't make them money. They are struggling right now.
If the Rezound was a Motorola device, it would have been announced that it was getting JB already seeing as a couple Motorola phones older than the Rezound and less impressive, have been announced as in line to get JB.
I would consider rooting it and flashing a JB rom, or whatever the term is, but I hear that the rom isn't perfect in that taking video doesn't work, along with a couple other things that don't work right.
I don't want to switch to JB if I can't use my camcorder or a couple other things.
I'm very happy with ICS, but it just really bugs me something better is out there that we should have and would be great on the Rezound, but HTC just says no.