Cats find many scents enchanting or interesting that we tend to find unpleasant or just plain offensive.
I had a kitten once that used to stuff as much of his tiny self as he could fit, head first, into my then boyfriend’s very smelly shoes.
My bf, unfortunately, had seriously vile, stinky feet and no matter how hard he tried to address the problem, nothing seemed to work.
So he always carried at least one extra pair of shoes and several extra pairs of socks everywhere he went.
When he came over, he’d leave the shoes he arrived in at the door and then hit the bathroom. He would wash his feet, change to clean socks and shoes and stuff the socks he took off into one of the shoes by the door and then put the shoes into a plastic bag.
Usually, by the time my bf was ready to socialize, the silly twit of a kitten would have deeply buried himself in one of the shoes and he’d stay there for ages. I think he sometimes fell asleep in there and he never seemed to have any problems with finding a way into the bag with the shoes and socks.
Apparently the foul smelling shoes were simply irresistible.
After the kitten finally finished enjoying the vile shoe stink and came out to play with us, I would have to bathe him, just to be able to tolerate having him in the same room as we were, never mind sleeping with us.
Your cat is certainly not alone in having a stinky shoe fetish.