Let's face it, men are competitive creatures. While the fantasy looks great in porn, and when in my prime I might have been comfortable with my body.
I am older now, and gravity has taken effect, among other things. I could only imagine being in a room with a great provider, and have some stud come walking in hung to the max. Not that I give a shit what he thinks, but rather what a provider would think.
" Hmm,,,,,old guy.....old dick.....gray hair......versus....young guy.....hot cock...."
Human nature being what it is, I would suspect the provider would gravitate toward the better cock.
Even if she did not do so, I would have it in my head that she was thinking it.
On the converse side, I sure as hell do not want to be in the same room, sharing a provider, with a guy uglier than me....
So there you have it. FMF for me.