It's not a choice he is consciously making, I can assure you. I've wanted to taste my own cum several times and as soon as I actually cum there is no desire at all to do anything with it.

I'm not going to get into the science of it, but it is all because of hormone changes at the moment of climax.

Bingo! That's almost certainly going to be at the heart of it.

As for any suggestions, how about rather than him doing the 'work', you hold your boobs to his mouth and tell him you want to see him lick his cum off them. If they're big enough, lower your head and lick with him. If they're not then cradle his head and encourage him, as though you're just getting him to nuzzle your boobs without cum on them. Maybe even tell him you want to kiss him afterwards as a bit of extra encouragement?

True...There is this moment when you are horny and build up to climax that you really want to taste your cum...as you learn to enjoy it, you have a longer time after you cum that you still want to taste it....I remember the first few times, I would have to actually shoot it in my mouth to enjoy it at that very moment...now I can do it right after alone or with my partner...I do enjoy licking my cum off her ass, stomach or tits.

I suggest telling him beforehand how much it turns you on and love it...keep up the snowballing and work up to it and get him to do it right away when/if he does do it.

any luck?