A lot of dudes legitimately don't know that's what it's for, or they don't understand just how many little splashes happen, or are too grossed out to touch public toilets, therefore feed into the spiraling feedback of desecration.
Just lift the seat with your foot if you don't want to touch it.
And (at least in the mens room) leave the seat up unless you need it, and if you use it, put it up when you're done. That keeps it clean for the next person.
The public bathrooms in Japan on the other hand are a fantastical heaven.