That’s because of the specific antibodies invovled.
I lost the link but I read that those who had natural covid infections, made more antibodies to the nucleocapsid protein s than to the spike.
It might be (hint: someone should do studies on animal models but the probably can’t get funding and won’t be allowed to publish) that antibodies to nucleocapsid proteins do not lend themselves to ADE, but that antibodies to spike proteins do.
Thank you, that is simple enough for even me to understand!