I don't use a loyalty card at any of the stores I shop at, and anecdotally, there's about a 50% chance that if I say "no" when the cashier asks if I have a card or want to create an account, I will later on discover that they've used a store code to give me the same discount.

This is without any prompting on my end, I never ask a cashier to do this for me.

So apparently it's common enough that some cashiers on-instinct just stick a store card in whenever someone says "no". It's common enough that none of them look at me surprised when I refuse.