Because we have gone for inept managers. In the rest of football and the real world, if a manager isn't producing results, he's out. Simple as. Let's examine a team who had recently gone through years of mediocrity similar to ours: Liverpool.
After Rafa, they cycled through:
Hodgson — Who was just terrible, no explanation needed. He probably had a plan and a vision but he wasn't getting any results. And we laughed at Liverpool.
Dalglish — Liverpool legend on and off the pitch, had previous success, and even won a trophy in his second stint. I'm sure he had a plan. They finished 8th, he got sacked next year, and we laughed at Liverpool.
Rodgers — The guy had them playing great football at one point and nearly won them the league. But then he dropped off and they started drawing and losing a bunch of matches, he kept referencing "they showed character" too many times, I'm sure he had a plan for Liverpool too. But he got sacked, and we all laughed at Liverpool.
Now they got Klopp. He started poorly at first but you could immediately see the style and plan he was trying to instill. He then gutted the shitheads, found players he liked, and eventually got them to playing fast paced attacking football, just like we used to do. They nearly won the fecking league and won the Champions League, beating Bayern and Barca along the way. Now they're one of the best teams in all of Europe, with a record start to their league campaign. They finally found their guy, and we're here watching them in envy. Guess what. Would he be managing them if the owners (who were criticized for being greedy just like ours) insisted on staying with Dalglish, or Rodgers because they had a little success once? Hell no.