Yeah but the point of that is to attract more men to the bar by having more women there. It's a marketing ploy targetting men who are looking for women to sleep with. Cheaper drinks also means that the women are more likely to be tipsy, attracting even more men. It's pretty sleazy overall but I guess it works.
The same dynamics don't work at a restaurant, you attract men to a restaurant by selling well cooked and well priced food, it doesn't matter how many women end up eating there or how tipsy they are.
It's a sleazy sexist business practice, but men out on the prowl for tipsy women who are easy to score with don't care too much. And I presume the women enjoy the fact they save money. In a restaurant setting it's a completely different context, people expect a bit of class there, and not blatant sexism and/or a promotion of rape culture or whatever.