Why do the SF Giants suck so bad?

Seriously.. I’m a fan only because I have a great nostalgia for all the games I attended at Candlestick Park when I was a kid. But for all the games I went to, the Giants pretty much always lose. I just went to the opening home game on Saturday and sure enough, decades later, they still stink.

Why? Why haven’t they gotten any better? I honestly want to know the answer.. is it a lack of resources to get great players? Mismanagement? Bad training? Does anyone know?