It's because you're most likely pathetic, needy, whiny, and spineless.
I'm not going to apologize for being harsh, but either you know what you're worth, truly believe it, and are willing to stand up for yourself, enforce your boundaries, and not be a pussy about it or you can continue to whine and then finally develop a co-dependent relationship with someone that will end in a spectacular trainwreck.
If you're having problems finding someone to date, the problem is with you, not them. It's in how you carry yourself, how little faith you have in yourself, and your attitude.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."