How clean are the park's public toilets?
If they are as filthy as most public conveniences, I do understand why people (of either sex) would rather go behind a bush.
But I agree, it is a filthy habit to wee just anywhere, and a potential spreader of germs.
The trouble is, and always has been, that mothers of little boys give up trying to persuade small sons to use the toilet before going out. Ringing down the years I hear, "But I don't need to wee" followed five minutes afterwards at the bus-stop, by"I need to wee." As it is easier to let a boy, even in a flying suit wee outdoors than a little girl who has to be undressed more-or-less, mothers, aunties, grandmothers, you name us, gave in and said "Well, pop behind that tree"
But that is no excuse for grown men, is it?
More public toilets, kept reasonably clean might help, but will probably have about the same amount of luck and users as the bins for putting dog-do, suitably wrapped, in!