Why the hate for jam bands? You know that jazz groups are essentially jam acts as well, right?

no fucking way. you're thinking "they both improvise, so they MUST be similar." The fact is, musically, there's a whole different thing going on in both. and it's not a straight line from jazz to jam bands. it's more like jazz > funk, disco > fusion > prog rock > jam bands.
Jam bands bite off all of those (and incorporate blue grass, techno, rap, etc. as well.) 50s sitcom and commercial music are also jazzy, but that's not like...some...weird requirement that I have to like those now just because it's talented and like jazz.
They use different instrument sets and largely different chord palettes, but it takes essentially the same skills to play these styles. Hate on the fans all you want, but denying the talent and musical ability of these guys is absurd.
There's no denying the talent. Phish is seriously fucking talented, especially. but it's not the same skills at all. The closer neighbors to jam bands are fusion and prog rock. Talent doesn't mean people have to like it. basically any nationally known musician/group has enough talent to get nationally known.

every dead jazz musician is rolling in their grave...