If you're not a Big name in the tennis field. Money is tough to come by. The pay structure should be equal and even more so given for the lower ranked players. And going back to the gender equality thing, the women should be paid the same. They attract girls and young and old women into the sport. They're ambassadors for the game. If every woman in the world decided to not to play, the whole tennis industry would shrink dramatically - The economy in this field would be ruined.
Best example is one of those muslim countries where only the men can play sport. It shouldn't be a surpise that they're not a sporting nation. There's virtually no consumer demand from women what so ever. And surprise surprise virtually no economy.