Hate against monogamous guys in the gay world...

I was just on a dating app (not Grindr) where a married open couple hit me up for "fun". All I simply said was "Thanks, but I'm not into that. I'm a monogamous LTR type here". They replied with "What a judgemental asshole! Good luck with that!"Has anyone else witnessed this hate for guys like me that are looking for monogamy? I didn't call them out or say anything mean at all about their relationship, yet I keep having open couples approach me and get super pissed when I don't want to have sex with them. Just curious if I'm the only one experiencing this or am I somehow being rude for politely turning them down?