They don't care about zoos or pedos, but pointing out that vaccine cards are easily faked actually threatens them. First it makes a mockery of their rules, second it could potentially scare away customers. Corgi Events is for-profit, so even above the normal "keep the con alive" financial considerations, they're not going to let something go that hurts the bottom line.
Probably more importantly, furries are generally left-leaning, which means they're in the "Covid has a 50% mortality rate and everyone should be mandated to get vaccines" tribe. Suggesting the use of a fake vaccination card marks that other person as a member of the opposing "Covid is a hoax and vaccines are how Bill Gates will sterilize the population" tribe. People are far more willing to put up with sexual deviancy than ideological opposition these days.