It only worked in the past when the UFC is still trying to corner the market. Alternative organizations were going strong, and it wouldn't do for the ex-UFC champ to appear on a rival promotion's program due to pay dispute. Today, the brand name is bigger than any of the fighters on their roster. With their marketing structure in full force, UFC can always hype up the "Next Big Thing" should anyone walk away. There are always hungrier fighters waiting to step in.
Cejudo walked? Now they have a newly-minted first time ever Mexican champ. Jones pulled the prima donna card? Now he is trapped between getting murdered by Francis or going back to LHW in shame after all the talk. So in answer to your question, nobody has that kind of sway anymore. While Dana did try to get Khabib to stay, no skin off his knees if Khabib doesn't fight again. They brought on Chandler, elevated Charles, and there is still activity in LW.
The only way a protest can work is if a large enough group of top fighters band together and go on strike. Fat chance of that happening, since everyone is looking out for their own interests first and foremost. Once they get the pay they want, screw the under-card right? Even GSP speaking up now, well, he has nothing to lose since he is retired.
Alternative way is if someone dies in the Octagon, or a high profile CTE case gets blown up by the media. This is the only realistic scenario I can see happening for fighters to finally get to unionize.