Jabba can just roll over and crush puny humans with his mass.Oh and some people have mentioned confusion/frustration that Jabba has a red/green melee attack because of his arms being Tyrannosaurus rex arms...and at first I thought the same thing and then I remembered his tail and I'm pretty sure he whacked someone pretty good with that thing once. But I can't remember.
Being expensive for a support character and one that won't be able to even contribute to objectives or board control, he needs a good attack to defend himself.