Why did the cat leave urine on my pants?

Because the cat's nose is very sensitive, it will find its own place to excrete according to its smell.

Cats and dogs always look for a place to excrete according to the smell at first. Maybe there is a smell on your pants that makes them think they can excrete on their own. I suggest you get them a basin, put cat litter on it and spray some inducers. In addition, pants should be tidied up or washed in time, and get used to it later.