Indeed. The "Coinbase" mining reward (currently 6.25 BTC per block mined) halves every 4 years. The theory is that the proportion of fees (currently only 10%-20

Indeed. The "Coinbase" mining reward (currently 6.25 BTC per block mined) halves every 4 years. The theory is that the proportion of fees (currently only 10%-20% of the total reward miners make) will increase and make up for the reduction in coinbase. Currently, a successful block makes 6.25 BTC * 45000 BTCUSD = 280k USD in Coinbase, or around 100 USD per transaction, plus a 10-20 USD fee per transaction. As Coinbase drops (or BTCUSD drops), users will have to pay around 100+ USD per transaction in fees, or the rewards to miners will drop and some will go offline, resulting in a reduction in difficulty and less energy wasted.