You must have been on the other side of this.
Can you not think of a guy you've met in your life who you like, fancy, have a laugh with, but you never "fell in love with" because whatever your magic ingredient was is missing?
As many posters have said, the why doesn't really matter. You are only focussed on the why because you are hoping it will be fixable. Sadly falling in love is not the same as a toy with a flat battery. It's never a case of Q: why doesn't he love me
A: because you don't wear enough blue.
You: Ok I'll wear more blue. Problem solved now he loves me.
The Why is usually thing you have no control over such as
he enjoys lots of sex with different women and won't settle down until he knows his time for that is over which will probably be when he's turning 50 and he'll take up with a model like 25 year old.
he will only marry a woman with a huge private income who is the daughter of the landed gentry
he's pre-programmed to only fall in love with a woman whose smile is exactly the same as his mother, who has naturally red hair and green eyes and whose skin smells like cabbage.
It's all random stuff you can't control.
The PP who posted about her similar experience where she pressed for an answer and got the brutal heart smasher of I never fell for you has it about right.
That's all it's about. He's not feeling it for you in the way you want and you can't change that.
He probably likes you, enjoys fucking you, enjoys spending time with you - but he probably has the same experience with lots of other women and tells them the same thing. You are all much of a muchness to him.
You are wasting your time. When he's ready and he meets his Mrs Right you won't see him for dust and you'll feel even worse than you do now.
The best thing you could do is take control and the high ground and walk away now.