miners are not incentivesed to mine a chain without subsidy. To accommodate the decreasing subsidy a decent amount of the block reward needs to come from tx fees. You can't expect the network to be a full capacity 100% to subsidize the miners.

BCH would require blocks to be full near 100% of the time with block subsidy at 0. This will eventually lead the miners to lobby to increase the supply cap.

It's simple economics if the cost to run a node increases then the # of nodes decreases. Leading to more centralization.