If we're going on the "hahah feminists just ruined their own jobs", how much work is that? Maybe a maximum of 3 days a year for the country you're in? I'm not sure if they do stuff on the practice and qualifying days, but I'll assume that maybe they do.
It clearly doesn't pay enough money to bring in any models we'd actually recognize. I tried to find out what the pay is but couldn't find anything. The few testimonials I could find all mentioned that it was in addition to their day jobs, so it's not enough to earn a decent living. Do we know any professional models that got their start being grid girls? If so, at least we'd have a career-advancement angle. In the meantime, I think there's something to be said that by framing it as though men are the drivers and the mechanics and the women are eye candy that it may discourage any women who actually are interested in racing at a young age from pursuing that career.
But let's not go with the "banning" language. FOM decided against having grid girls at their events. There's nothing preventing these women from working a myriad of other racing events, or autoshows, or frankly just about any major convention that still hire them. One series decided that they thought it financially or otherwise benefitted them to make this call. Otherwise, the "banning" idea sounds just as stupid as the confederate flag people.