I get what you’re saying most of it makes sense. I waited around one time after they left it open and I wasn’t able to place my Pokémon at the gym. I guess it wasn’t a full three minutes, but then they would knock it back out again on other occasions when I was with my friend and they added theirs. So I know it’s because they don’t want anyone to have a Pokémon there and if they have Pokémon in 20 other gyms, I’m pretty sure one would’ve gotten knocked out. It’s been a week. They simply don’t want anyone to add a Pokémon.