Why would a guy leave your Facebook request on pending?

Ok first world problems, but say you’ve had previous attraction, the guy has 776 friends on Facebook (not that fuss then) and you send him a request but he leaves it on pending.

He is a coworker, but I’ve sent other coworkers requests and it’s been accepted in hours if not a day. He does have a girlfriend, but I’m not trying to pursue anything, just be friends. Why not decline if he doesn’t want too, why stay in the grey with pending?

Why would a guy leave your Facebook request on pending?
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