It’s basically the flip side of the Krispy Kreme giveaway: behave like a responsible member of society during this public health crisis, get a goodie; be a selfish* or deluded arsehole, no cheap concert or free donut for you. In either case, no-one’s going to look too closely at the CDC cards or care if they’re forged.
For now, it’s fairly low-stakes stuff in the absence of actual enforcement mechanisms. That’s going to change as the vaccine passes kick in and the willfully unvaccinated – especially entitled white people --can’t fly or go to a basketball game. Conservatives and Libertarians know it’s coming, which is why they’ve started doing everything (except actually discussing legitimate ethical questions regarding underserved communities) to sow bad-faith FUD around the concept.
And of course, the Death Cult Party politicians in power are already passing spurious laws against vaccination checks to pander to the Know-Nothings.
[* apologies to the AynCaps and Objectivists out there who think selfishness is a good thing]