Well, because it's partially true, in the sense that a white conservative male could be guaranteed a certain minimum lifestyle, job, and opportunities, despite gross inadequacies.
All white men needed to do was dutifully support the Plutocracy and their guard dogs in the Republican Party and a good job, decent pay, a social safety net and freedom from maltreatment from the police state would be theirs. White Privilege used to mean there was a certain floor under which no white male would be allowed to fall.
But, Capitalism cares not for national boundaries or peoples or social contracts, once the American Worker became too expensive the American Worker needed to be downsized.
Since the Reagan Revolution their Corporate Overlords have broken the contract they had with white men and now conservatives are being treated by Capitalism and the Corporate State the same way blacks, women and immigrants have always been treated; as disposable goods.
White men don't like it, and have been searching for a reason why their standard of living has gone down despite working longer hours, being more productive, having to pick up extra jobs to supplement his declining earning power, while his wife also has to work not as a luxury but as a necessity.
"You work three job? Uniquely American isn't it. I mean, it's fantastic that you're doing that." - W(orst POTUS in history) 2005.After dutifully supporting George W(orst POTUS Ever) Bush no matter what evil and awful War Crimes the Bush/Cheney Regime committed or the $10 Trillion dollars Bush stole from the American people or the lives of hundreds of thousands of Americans their warmongering cost, now Conservatives want to know what happened to the American Dream.
But, it's too late. For 35 years, Toxic Right-Wing Talk Radio, Faux News, and now the Incestuous Conservative Internet Bubble has been making sure Conservatives were suitably brain-washed to be outraged at Steak-Eatin' Young Bucks, Welfare Queens, the Lucky Poor, Teachers, Women, Gays and Illegal Immigrants instead of America's True Enemy, the Plutocracy.
"The first step is, we're going to deal with collective bargaining for all public employee unions, because you use divide and conquer.” - Wisconsin Governor and Presidential hopeful Scott Walker.Thus, despite stated Republican Goals of stealing Social Security, "phasing out" Medicare, reducing Workers' Rights, eliminating welfare for the poor while increasing it for Corporations, and turning every American into a 3 Jobs-a-Day Wage Slave, conservatives still support Republicans because conservatives suffer from battered spousal syndrome and they can't break free of their abusive Right-Wing Masters, who ensure they vote to enslave themselves by saying,
"I don't want to make blaaack peoples lives better by giving them somebody else's money," Rick Santorum in Iowa 2012.Now, a sizable portion of the right-wing voting base are absolute racists who hate people of color, and these are the ones fueling Donald Trump's "popularity". Trump, an absolute joke of a human being, is leading by saying what every Republican, since Nixon crafted the phrase Law & Order, has been saying just without the code words and dog whistles.
This worries Reince Priebus, the RNC, the Koch Brothers and the Plutocracy because appealing to the racist vote is something they would rather do behind closed doors, similar to Mitt Romney's infamous 47% Speech.
So, I hope Hillary Clinton (or whomever wins the Democratic Nomination) does not make the mistake of tacking towards the Right in order to slice of a portion of the Fragile White Abused Conservative Whiner vote. It's a losing formula. Democrats need to keep the focus on what they stand for, point out Republicans actually hate the angry white man they've been cultivating for decades, and demonstrate that the Reason White America feels it's lost the American Dream is because the Republican Party has stolen it.