I think this analysis assumes that Dwarf Fortress has reached only a small fraction of its total addressable market (that is, the space of players who can enjoy DF without large improvements to new player onboarding). Any fixed-price offering risks cannibalizing Patreon subscriptions, whose expected LTV is probably _much greater_ than $19.

Their chosen tradeoff makes more sense if you think of it as "subscriptions versus one-offs" instead of "sales versus donations".