One of the biggest questions I couldn't answer when onboarding people to Hive is that I didn't know where the funds for the Hive reward pool were coming from.
Luckily @mraoul took some time to research it and found the answers in the Hive FAQs :).
You can read more about it here:
But there is not a fixed supply of Hive. Starting with the network's 16th hard fork in December 2016, Hive began creating new tokens at a yearly inflation rate of 9.5%.
Out of the new tokens that are generated:
65% go to the reward pool, which is split between authors and curators.
15% of the new tokens are awarded to holders of Hive Power.
10% of the new tokens are awarded to the Hive Proposal System.
The remaining 10% pays for the witnesses to power the blockchain.