Same reason Jessica Yanniv went to small immigrant parlors. Misogyny and racism go hand in hand. It's also practically handy as they're less likely to be able to mount good legal defenses if it came to that.
Bringing Jessica Yanniv up with regards to the spa debate brings this to mind.
The argument that the spa owners have the power to shut down undesired activities at the spa is technically true. However, defending oneself against allegations of discrimination can be expensive and many small businesses can't afford to do so. So they might be afraid to attempt to enforce a behavior code against some demographics unless they have rock solid proof that no one can dispute. Complaints from another customer do not qualify in this manner.
Jessica Yanniv, I believe attempted to weaponize anti-discrimination law against a minority she did not like. Did she succeed? She lost in court and was ordered to pay recompense ($6000 split between three businesses). But at least two of her victims were forced out of business by the complaints. (And apparently, she is suing the ones who won their case against her.)
So yes, Jessica Yanniv is an example of why someone might be hesitant to try to enforce standards. It's not just this type of thing where this applies to. Kroger didn't want it's managers to push too hard enforcing mask policies for similar reasons.
Even if you win in court, you can lose. Reputation can be damaged by social media complaints that never go to court.