You only have to read the posts on this site over the last two years in which the Nebraska fans predict blowout victories over UCLA to verify what I have stated.
UCLA - the program itself - is irrelevant in regards to Nebraska's problems. Both games were simply more examples in a long line of 'what the hell are they doing' Nebraska games. And as a member on this board for the last five years (significantly longer than yourself), I have no recollection of "Nebraska fans" predicting blowout victories. Were there some people that felt this way? Sure. Was it the majority of the fan base? No. This is a very, very poor generalization, whether intentional or not. The Bruins, like every fan base in this history of sport, have jackwagon fans that say ludicrous things, too. Like the way I saw quite a few Bruins fans bashing Baylor last year before they physically manhandled UCLA like small children. Let's not go throwing stones in glass houses, OK?
Back to the OP, there are a few reasons this game was the tipping point for many fans, and why this loss could be considered one of the more devastating in the Pelini years. First, the loss once again showcased issues that have been prevalent for a couple of years now. Mainly, a lack of fundamental, disciplined football play and team that's mentally weak. Something goes wrong, the issues snowball.
Second, UCLA, like just about every other team Nebraska has faced over the last few years, had comparable talent. Nebraska has really only faced a couple of teams that I would say had a clear talent advantage, and UCLA isn't one of them. Same with Wisconsin. Not to take anything away from these teams, because they're good football teams, but they're not as good as Nebraska has made them look in recent years.
Third, and back to the mentality side of it all, Nebraska gets way too high on itself and consistently needs a kick-in-the-pants. Embarrassing loss after embarrassing loss, fans hear that the Huskers lost focus, didn't fight hard enough, took their foot off the pedal, or whatever other excuse they can come up with. If Nebraska football were a house, it'd be missing a couple of support beams.
Lastly, fans wanted to see that this team had overcome these issues. If they hadn't, it'd be evidence supporting the claims that Pelini may not be the right man for the job (whether that's fair or not, it's happening). And now, Nebraska has no real way to test itself until they play Northwestern IIRC. They have weeks of football against teams they should be heavily favored in, so if things go as they're supposed to, we're not going to learn as much about this team as we'd like.