Unable to feel satisfied from masturbation

If I fantasise without masturbation, I tend to get a lot more pleasure, but then as soon as I try masturbating all the actual arousal kind of goes away and is replaced with a mildly pleasent genital sensation. But the physical sensation is actually a whole lot less intense than if I just think about something instead. Because I'm not that aroused during masturbation if I orgasm it isn't really that good, and the arousal from before just returns pretty much instantly when I stop touching and there's no satisfaction whatsoever. What do I do? Why do I stop being aroused as soon as touch happens?