probably because when i was growing up as a millennial every pool went from 3ft to 8ft in a matter of steps. the ones that are alive today are the ones that learned to swim by nearly drowning from slowly drifting into the deep end unattended.  zoomies grew up in a neutered world where pools don't go deeper than 5 feet if it's not diving. they would never even be unattended as children so there was no reason to learn to be a good swimmer for the children that never went outside in the first place.
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