The American Federal government will not allow for the legal use of PEDs in professional sports any time soon. Regardless of what the fans really want, there will always be a rather large morality hurdle that the politicians will rally behind.
Even the WWE implemented drug testing because of political and public pressure to keep a clean image. They are just an entertainment company, but the pressure to keep PEDs out proved to be too much.
The main reason for this is because of the potential influence on minors to experiment with these drugs, along with the American war on drugs to begin with. The other reason has to do with the negative impact that long-term drug use can have. The WWE has had numerous stories emerge regarding PED use, recreational drug issues, and widespread use and abuse of painkillers and such. The WWE really started to feel a financial impact when various lawsuits, lobbying, and political/public pressure started to mount.
The UFC stalled on this issue for a really long time but eventually had to embrace the USADA when the public and the media pressure increased especially regarding TRT. Vitor was one of the leading names to bring about this change. Instead of managing his use of TRT in a respectable way he tested far over the limit in Nevada basically embarrassing the NSAC. Dan Henderson, on the other hand, appeared to be managing his TRT use quite admirably and didn't test over his exemption limit. Ronda also couldn't stop making comments about Cyborg which brought about a great deal of negative focus from both fans and the media. The UFC had to make a stand with all of this stuff being kicked up by the storm and the USADA was brought in.
As much as some people might like to see PEDs be widely accepted, it will not happen in the near future.