My understanding is that mining is an essential function in processing the public ledger, and folk are incentivised to do this by the reward of bitcoins at periodic intervals.
My question is: When all BTC21m have been mined and released into the wild, what will incentivise folk to carry on 'mining' and verifying or processing the bitcoin public ledger?
Step one: Be aware that "all
BTC21m won't be mined and released into the wild until approximately the year 2140. So, while I can understand you having some concern for your children or grandchildren, I personally believe that technology will advance in the next 100 years beyond anything we can predict today. It is really impossible to guess just what bitcoin will be like by then.
Step Two: Be aware that the miner's block reward consists of both a block subsidy (currently 25 BTC) and the transaction fees of every transaction that they add to the ledger. Over time the block subsidy shrinks (it is cut in half approximately every 4 years) and (if it gains popularity) the value of the transaction fees increases due to more users paying fees. Eventually the fees will be greater than the subsidy. Perhaps at that time, we'll stop calling them "miners" and start calling them "transaction processors", but the job they'll be doing will be the same.