They are short.
Seriously? This is the top trending news today? Alright let's talk about that then. Serena "The Catsuit" Williams just turned the world around again wearing a one piece that showed two-pieces-of-her in all its glory.
If you really believe this is "inappropriate", well how about this?
Seriously, you'd have to be quite dumb if you believe most men care about women clothes ethics when they look at them playing. Hell, I'd do a survey just to make sure I'm not crazy. If you want tennis to be appropriate, stop hiding your head in the sand and believe their outfit was not expressly made for men to salivate.
On another note, I'm not even sure I'd believe you if you were to tell me the women were not forced to shout when they serve. Come on, now. Anyway all this to say I don't care about Serena's shorts, they are fine by me and potentially less sexually attractive to the consumer.
I believe a lot is hidden in women sports, starting by the fact men own the riches in many facets of the sporting world - women sports included. I wouldn't be surprised if, in a decade or so, a lot of women got out of the closet about what were asked of them back in the days.