I was always terrible at picking up on hints, but even when I did get the hint I was generally either not interested in pursuing something, too cowardly to pursue it, or I had a preference to go about things a bit slower.
Sometimes women can be attractive and hint a lot, but once you've burned yourself once or twice you realize it's better to take things slow than to risk getting involved with someone more crazy than you can handle.
Amongst people I am closer to and actually like I am absolutely oblivious at times, but I would much rather err on the side of friendship.
I think we always assume our own communications are super clear, and we blame other people when they don't understand. That goes for flirting, but also everything else involving two or more people trying to communicate.