I can only speak for myself.
My horniness level is far from universal. How I feel with one partner is different than another. Sexual chemistry plays a huge part in how I feel.
For the record, I betcha the guys have self esteem and confidence issues because of it too. Just because they are saying "no" doesn't mean they arent battling with the same thing.
Solution - no idea. I can't fake it till I make it. There is either a raw unadulterated lust or their isn't. It can come and go in waves I suppose, but it isn't something anyone else can control.