Up until men are 40-ish they're ready, able, and willing to sexercise anyone anytime anywhere as 'it' still works really well and sex drive is still high.

I think age is a big factor in this.
Up until men are 40-ish they're ready, able, and willing to sexercise anyone anytime anywhere as 'it' still works really well and sex drive is still high.
Once they hit 40-45 'its' functioning begins to decline for most. That's the time men say "I've finally mastered it!!"
They haven't, it just doesn't work the way it used to anymore and this decline tends to increase with the years.
It still functions, but the steel has gone out of it and it takes (much) longer to reach the finish line.

I guesstimate that's also when it becomes easier to say "I got a headache".
Maybe they just don't feel like the hassle of attempting to wake it up or to take a pill for that...

And I know some are lucky and don't have these issue but generally speaking...

Just Google "Kegels". You will mostly find exercises and tips for men, NOT women, in order to improve the function of 'it' or to not lose that.

Never met a men under 40 that wasn't interested in an opportunity to have sex. Being very attracted to the receiving party doesn't matter so much at that age, just the chance to get their rocks off.