Why was Blackwell's medal so late?

David Blackwell was awarded the National Medal of Science posthumously, 4 years after his death in 2010 at the age of 91. At the occasion President Obama gave the award to Alexandre Chorin and Thomas Kailath as well, among other recipients in areas I am less familiar with.

All awardees produced great work that we all should be proud of, basking in reflected glory. But it's not the case that each one single handedly changed their fields, as did Claude Shannon or Rudy Kalman, to name two earlier winners whose work I am familiar with.

Why then did Blackwell's medal have to wait 4 years after he died, and not at an unexpectedly young age? Sadly, the only conceivable reason is that racism still affects America, even at the highest levels of science.

And if someone adds that, yes, Blackwell was African-American, but he was also a Bayesian, then I suppose the juxtaposition might be taken as comment on the intellectual basis of the anti-Bayesian or frequentist movement.