Because they're fukking you already anyway. Just because you currently have the means to weather a storm doesn't mean that your situation can't change in the blink of an eye or that you have been duly compensated for your past efforts.
As the poster you quoted said, why is it always expected that individual citizens bear the burden of "doing what's best for the greater good" and never the larger institutions and businesses that put us into these predicaments in the first place?
Reminds me of the whole littering/recycling campaign movement. As an effort to push back against regulations to stem the overproduction of waste and environmental damage (which would hurt profit margins), companies pushed for a public effort to place that responsibility on individuals, instead of these corporations taking responsibility for a societal problem they created.
Saying you're cool not receiving tax payer funded relief because you rather donate it to someone in need completely misses the point. It's no different than that asshat Whole Foods CEO suggesting that workers with ample sick/vacation time donate it to their fellow employees who don't have any time left accrued........instead of just giving your damn workers the time they need to so they won't die trying to make you even richer than you already are