If you really want to get technical about it, Gundam should've never went further than Char's Counterattack or maybe even further than Tomino's original storyline where Amuro get's killed off.

That said, I guess you could blame wimpy protagonists on japan's subconscious feelings of inadequacy from losing the war but there's also the fact that mecha anime hasn't been all that relevant in a long time. I mean you've got some shows that are made for nostalgia's sake and gundam itself pretty much just exists to sell model kits.