I have found myself in that position often. Waiting in the sling only to have someone cum in, maybe finger my ass and then walk away. Hard to say what makes them leave or why they choose to stay. I'm not everyone's cup of tea, I'll admit, but when I am in the sling with a hood or blindfold on, it clearly signals that they are to use my hole with no concern for the rest of me. I HAVE found that it's often a matter of timing - the later in the night I hop in, then more guys are ready to play. It may be the "is there someone hotter I haven't seen yet" thing or it may be the "I don't want to cum yet" thing as much as not finding me attractive. I used to be upset by it, but now I just wait for the next cock! there's ALWAYS another cock. ....AND, if I've been waiting in the sling with no bites, I hop out and walk around or hit the gloryholes. No one likes a sling lizard.