Basically, because if I continue to be "competitive" it will only suck the value out of my team until I can't compete. The best example of what I'm saying is...
Got sick of tanking. Tanking sucks. Bleagh. Bought players. Going to win things. Won't win all the things. Will be sad. Bleagh.
If everyone played to be as competitive as they can every season, success would rely on training and tactics. But that's not how it is... The most effective tactic is to tank until you can buy your way to the top. There is nothing wrong with it except it means seasons of doing nothing while you save for your season to shine. If you can't win, don't waste money trying...