I don't have any definitive answers, but from what I've observed amongst my own family members (6 sibs), all Baby Boomers, it is because people are increasingly discovering that you don't have to argue with your political opponents (i.e., present cogent arguments backed up by facts) if you instead demonize them.
Regards,
And the easiest way is to call them a ‘racist’, there’s no point in arguing with a racist.