The swastika is a holy symbol in Hinduism. Absolutely not associated with genocide for a thousand years.
The Nazis adopted it, and now Swastika = Nazi.
The hammer and sickle was used to represent industrial workers and farmers to unite against the bourgeoisie. The USSR adopted it, and suppressed Eastern Europe under abject authoritarian rule for half a century.
For individuals who have had to go through that crap, yeah... Why would they not hate it as much as the Swastika?