As many have pointed out already, for whatever reason you have for wanting to eat your cum before you actually cum, such as it looks hot to see it on video or that doing so will keep you horny, we all come (no pun intended) to realize that one of nature's best protective mechanisms (to immediately lose your sexual desire after orgasm) kicks in and you have absolutely no desire to do so when you actually cum. So now you have to ask yourself, why do you want to eat your own cum, and what will it take to get yourself to actually want it and enjoy it.
For me, I had to think in terms that my cum is not about me being horny but rather it's my own body's expression of its muscle and masculinity. In other words, it's about acknowledging and enjoying my masculinity. The benefits I now enjoy in being able to eat my own spooge is that I impress any and all male partners. Females, by and large, do not like my eating my own cum, sometimes even going so far as expressing homophobic comments. But I just see it as their loss.
To sum it up, why I do it is because there's nothing quite as awesome about my own masculinity and all of its manifestations than my own muscle cum. As for the taste, once I got past the initial reflex to not want to eat my cum, I realise that it really doesn't have much flavour at all. It has a good aroma, but not that much flavour.