Flanderization

In  most modern media, every character is an idiot whos always trying to make others laugh. Old favorites of mine like Family Guy have fallen victim to flaznderization. My favorite example of flanderization is Brian Griffin, once the best character on the show, now someone I look at very disappointed, Why do writers for these shows take one character trait and use it to ruin the character entirety? It's not funny most of the time, and makes viewers like me lose intrest.