Crispy tostadas originated a long time ago, but Americans turned them into hard taco shells in the 1950s. They no longer make sense in social settings.
It takes a little sleuthing to figure out if Americans do or do not like hard-shell tacos. And one must do a fair amount of research to find out why hard shell tacos ever existed in the first place. But what we were able to find is that soft shelled tacos seem to have won the hard vs. soft battle some time in the recent past.