Well, there is a ton of ped using athletes out there so the question is... who is unfortunate enough to be caught
Usa athletes (just for example, don't get upset with it
) tends to have a lot of "protection" on big events (mostly Olympics) so as other big/great/influential countries... nothing new there... it was very "political" back in the days and now is basically the same but with a lot of $$$$$$ "flavor"
Tennis (unfortunately) isn't excluded from that (imho very dark & simply unfair) side of sports but there's a lot of $$$ going on and when's a lot of $$$ going on, "shady things" usually stays "under the surface"