The problem with the Ultimate universe was innately inherent within itself, its own conception, from the very beginning. So many of us have been saying this right from the outset. The notion of the Ultimate universe was to create a modernized, clean slate for iconic characters free of the continuity that often scares readers away, yes? Well there's the problem, right there in that sentence. There is physically no way for you to be free of continuity in a serialized comic. That's the whole concept of an ongoing story, that it builds on itself, that events from the past matter to events in the future. It has nothing to do with not focusing on the correct characters or adding too many characters or whatever. Unless you make the story finite, there's no way to stop continuity from accumulating.
Look at Ultimate Spider-Man; it's got something like over a hundred and twenty issues already over the course of more than eight years. Even if you view it within its own contained microcosm, it's still got more continuity and backstory within itself than can ever be casually explained to any new reader, or even most old readers. Moreover, Peter should have graduated from high school twice already in that timespan, so no longer is the comic even "modern," merely recycling elements of itself. So that's both of the goals of the Ultimate line -- continuity-free accessibility, along with modernization -- that USM could never achieve, and never could achieve in the first place, and not because if failed or anything, but because it is what it is.
Suppose we use your idea, Blader, and only focused on iconic, significant personalities of the mythos instead of cramming in more and more characters to "Ultimatize." Well, then, now we would have the Green Goblin or Dr. Octopus or Kingpin or whatever attacking Peter's school or kidnapping his friends or robbing banks...over...and over...and over...and over..and over again. The same sorts of stories about the same sorts of personalities...how many different ways can anyone come up with for the same batches of characters to do the same bunch of things to each other? And obviously it's not just a problem with the UU; mainstream cyclical comics face the same problem with every single new issue. The difference is that the Ultimate line was created for the expressed, pointed purpose of not having that problem. Which is impossible. There was no way. The whole point of the Ultimate Universe was and is to be fresher and newer and more accessible than the mainstream universe, but there's no way that anything can be always new. It literally defies the definition.
And some of us have been saying this, from day one. That the Ultimate universe has no real point, it's just some alternate universe, and it could never sustain its own steam. And it's not like some profound notion or something, it was always the case of stating the obvious. And lo and behold, here we are, eight years in...the Ultimate universe has no real point, it's no different from any other alternate universe that Exiles might visit or something, and it hasn't been sustaining its own steam.
I guess what I'm really trying to say is...is anyone actually surprised?