What will happen to steem

I am thinking a problem about steem. The number of steem people is increasing. And accounts are generating new steems. So one day there will be huge supply of steem. There may not be enough buyer. What will happen at that time.

In coinmarketcap it says total supply is 291,399,858 STEEM. But if its not fixed how can it be written there.

When I made my account last year I got 15 sp free and with that if I click upvote I would get 0.01$ but now I have over 30 sp but I get 0.0$

So in future will there be reduction in reward to keep price stable. Is rewards like mining getting harder day by day.

I am confused can anyone provide me article or say in simple way.