Three things:
1.) Ralph isn't senile, he's always been this way. He fired Polian fifteen years ago when he was a much younger man, and other than a brief burst under Lou Saban in the 60s, has always hired subpar personnel. Age may have made it worse, but it's not like he was a genius football man who lost his faculties. He's been a bad owner to work for and never was any better.
2.) Jerry Jones just won his first playoff game since 1996. He got on a hot streak in the early 1990s because he backed into greatness from the Herschel Walker trade, and hasn't been able to recover until now. And for the most part, coaches don't want to work for him: it's why he has Wade Phillips. He briefly got Bill Parcells, who quit a few years in.
3.) Snyder has a similar track record. They haven't done much at all since he took over, basically, the team has been the Bills with a little bit more luck and without the Patriots in the division. And his last coach was Jim freaking Zorn. He finally agreed to give up all the authority to Shanahan, who took the job. Ralph wasn't willing to even to do that.