As block reward decreases, miners will be dependent on transaction fees to suffice for their electricity costs. By then, if the price of Bitcoin isn't high enough, it will lead to a further reduction as miners abandon their business because of the lack of profit.
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Further reduction?
Further reduction in what? Why would it matter if some miners abandon their business?
If a sufficient amount of miners leave the Bitcoin network, then there would not be enough to confirm pending transactions and mempools would grow massive. This isn't efficient.
The more miners leaving, the lower the difficulty will decrease. This will open up possibilities for other people to start mining again. If it drops low enough, you will even see people starting to mine with their CPU/GPU's like back in the day. Bitcoin mining for less coins are still profitable, if more miners leave and eventually miners fees will have to make up for the gap. In theory transactions needs to multiply to make up for the loss, when Block rewards are reduced with every Halving. < The Mempool is very congested, so it looks like it is working > ^smile^