I think the real turning point was Home Improvement with Tim Allen. Prior to that, a lot of these TV dads were either kind of unique for their time or such blatant caricatures that nobody would realistically view them as somehow characterizing an actual father figure (Al Bundy, Homer Simpson). Tim Allen, while cartoonish, was presented as more realistic. While sympathetic in some ways, he was an absolute, bumbling fool. He tended to be the butt of nearly every joke on the show and was about as incompetent as a person could be. The only semi-strong male figure on the show was Wilson, the wise but faceless neighbor. So the only competent male figure was a dehumanized, faceless figure nobody could realistically relate to.
It seemed like, after Home Improvement, most family-based sitcoms that followed used the same basic structure of a bumbling fool of a dad/husband surrounded by similarly foolish males who either relied on their wives & girlfriends to resolve all their problems, or were only successful by the dumbest of luck or through some other sort of providential intervention (Everybody Loves Raymond, King of Queens, etc.). Many commercials even took on a basic pattern of the foolish/mindless/inept male countered with the confident, omni-competent female who found the keys, fixed the car, saved dinner, etc. all with a wink and a “not again” roll of the eyes at her impossible “man.”
Combine that with the movies of Adam Sandler, Will Ferrel, etc. which all seem to follow the same basic formula of the bumbling man-child whose only successes are at the most inane, childish endeavors and you’re left with the current view of a “real American male” as some confused idiot blindly stumbling through life, whose only real successes (outside of passing grade school again, out-drinking the local frat boys, and coaching the local kids soccer team to a losing season) can only be attributed to his wife/girlfriend and/or children.
It’s no wonder that, in my experience at least, so many “adult” males strive for these low goals and struggle not to exceed them, while many others (men & women alike) look down on and are even offended by a man who strives for something more than a kick-*** party, an awesome beer bong, and marathon sessions of Halo or Rock Band.