So, if the miners receive bitcoins as their rewards after solving the puzzle, how do those bitcoins get into public circulation?
What I mean is how are we the public able to purchase these new bitcoins that are mined? And what prevents the miners from hoarding them and deciding not to sell them?
at this stage it no longer matters. miners do not mine much. over 19 million coins are out there.
the answer to your question is:
most Miners can not afford to mine and hodl 100% of their coins.
If all gear is s21 it earns 9 dollars a day and burns 90 kwatts so if all miners are 4 cent watt cost they burn $3.60
so 9.00-3.60 = 5.40 per unit profit
they need sell at least 3.60/9.00 or 40% of the coins they mine.
So at least 40% go back to market