You made it simple to understand, the old "where does the money come from" is always hard to explain to people since they have their brain configured to the current fiat system and Web 2.0, especially when the question is about STEEM and their current understanding of what "inflation" is isn't the one we normally use in the crypto community... I normally say something like, "The value of it is all based on supply and demand and demand comes from people seeing value in it..."

I do think however that all Steem dapps should put ads and use their ad revenue to buy and power up STEEM and upvote their users to decentralize the SP throughout the more active users, this would provide more demand, less supply on the market and would decentralize the SP hodlings more. Doing this would provide a much easier way to explain where the money comes from... ad revenue being stored on STEEM.

Regarding the upvote part, can you believe that there are still some steemians who have been in this for a long time(3 years +) that didn't know that the reward pool comes from STEEM's inflation...