When someone tells you "you can have this if you pay me", they don't mean "you can also have it if you don't pay". They are implicitly but clearly indicating you gotta pay.
It's as simple as that. In common use, "if x then y" frequently implies "if not x then not y". Pretending that it's some sort of a cognitive defect to interpret it this way is silly.
In the original studies, most people made an error that can't be explained by that misunderstanding: they failed to select the card showing 'not y'.
From my armchair this feels relevant:
> Decoding analyses of neural activity further reveal significant above chance decoding accuracy for negated adjectives within 600 ms from adjective onset, suggesting that negation does not invert the representation of adjectives (i.e., “not bad” represented as “good”)[...]
From: Negation mitigates rather than inverts the neural representations of adjectives
At: https://journals.plos.org/plosbiology/article?id=10.1371/jou...