If you were going to pay tennis players according to television ratings, it would make the pay scale incredibly complicated. For example, a women's match featuring Serena Williams V Naomi Osaka would be likely to receive higher viewing figures than a men's match featuring players like Evgeny Donskoy V Mirza Basic.
It's better to award pay based on sets played. On the ATP tour and the WTA tour, players generally play best of 3 sets. It's only in the Grand Slams and a few other various tournaments where the men are playing 5 sets. In those tournaments, I agree that if women are only playing best of 3, they should not receive equal prize money. It should either be awarded to scale or they should play best of 5 like the men do.
@Fusion: It would be complicated because you'd have to calculate the viewing figures for every individual match and even then would you base it on the worldwide audience? The US audience? The audience in the country where the tournament takes place? Or just how many people actually show up to watch it on court? If you're going to judge Grand Slam prize money by stadium attendance, well in the early rounds, most courts showcase a mix of men's and women's matches and the crowd typically tends to show up for the entire day/evening session. So, how would you figure out who really wanted to see the women's and who was only there for the men's? It's untenable.
Other sports don't work that way. A Master's winning pro golfer doesn't have his prize money increased or decreased based off of how many people watched him win.