Disney doesn't offer it and the hotel costs are not that much different. I really think that is part of the problem. 2 parks and tons of people jamming express pass lines. The cost of EP really isn't factored in to the hotel all that much as you'd pay the same price at a Disney property without it. You can't pack hotels for two parks with express pass guests and then continue to sell them to other guests and expect that lines won't be long.
I'm sure there are plenty of people staying at the deluxe hotels who are spending less time then they otherwise would at volcano bay because express pass is not offered there. If they can eventually figure that out, that would spread people out more.
While I haven't been to universal in years, I don't think the conventions are factoring into the express pass problem, regardless of what the hotel caters to, there are plenty of people that will book whichever of the 3 hotels has the best rate for when they are going just to get the express passes.