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Witness rewards were about 5x higher pre-HF16 as I noted elsewhere. Costs were also much lower (smaller blockchain), and the initial witnesses were all early adopter whales who didn't really need the rewards. In case you don't know power down used to take two years so the rewards (which have always been 100% SP) weren't even all that accessible to cover costs (plus for a while, no exchanges). Witnesses covered costs out of pocket, though again the costs were much lower (any cheap server would suffice).