Because cars are a predominantly man's territory, and most men know basic stuff like that by the time they're adults from their fathers. An all woman class breaks down that barrier and tells them cars are for them too, it can also tailor the class towards woman's interests like what to do if your car breaks down. How to quickly change a tire if you're on the side of a road while being safe. It's like having a man's sewing class, sewing is a good skill and they can tailor it to men's interests.
As soda mentioned, men can get patronizing about explaining car troubles. Though, I do have a mechanic that talks to me like an actual human and explains what's going on.
Honestly though, I already know about most of that stuff. The only basic thing I can't do is change the oil on my own because I have nothing to prop my car up.