It's not as odd as you may think, that's why the guys you requested videos from are pretty cool with it. It may not be common but it's not unheard of. Just many don't talk about their fetishes and what turns them on, so we don't hear about many things unless we move in certain kink circles. The LGBT "community" is full of subcultures within a subculture.
My interests in public toilets stems from it's where I first noticed men's genitals and later on discovered homosexual sex. It's where I saw my first uncircumcised dick in real life peeing next to me. I knew what it was in theory and had seen diagrams and drawings in text books and library books. Till one day there it was right there next to me urinating while I snuck glances out of the corner of my eye!
Toilet functions are a very personals and private matter in our Northern American society unlike some other cultures. In the public toilet/shower room setting the private becomes more communal and maybe even social to some degree. As a young pubescent male these things intrigued me. I might have hated Gym Class but I loved the obligatory shower afterwards. I recon this is where my voyeuristic tendencies all started.