People who would would rather let the person receiving the tip decide if the government deserves a cut tip cash. And as others have said, using the employer's card processing flow gives the employer opportunities to do less than great things.

A lot of bars and bar-adjacent restaurants outside of SF and NYC rely heavily on cash.

Even when I pay the check with a credit card, I will frequently tip in cash at a sit-down restaurant or bar (which I’m not going to at the moment as they aren’t much fun currently, but hope they’ll return in force this year).

Cash is better the employer can abuse tips given via cards - and screw the employees