Those were rare and for charity, this is the second microtransaction within less then 30 days.
And it occurs to me that Spelljammer & DL monster Compendiums my have been intended as the first, but folks were so unhappy they decided to drop them for free instead, waiting till they had D&D Beyond.
There will be more for pay Monster Compendiums and Adventure Atlas', along with others types like maybe Volo's Races and Tasha's Classes or something. Maybe even entire small settings. We could even get more Eldraine this way with its own adventure Atlas.