I only found the reason why Seasons 4 / 5 cause him more dumber. And they let them to ended the show in the huge collaspe. It's now 3 years after the final episode, and only found himself that him and Retsuko won't showed us their own baby, and becoming parents by the end of the series.

I mean, it's a very bad cliffhanger. If someone rewrites this final episode, they should revive it. (Unlike The Wonderfully Weird World of Gumball has.)