two things, firstly, currently there is a block reward for finding a block, this was and still is the main incentive for miners. Currently the reward is 12.5 BCH per block found. every few years this reward halves (next in 2020) and in the year 2140 the reward will be gone altogether (very long time from now). By the time it runs out, the idea is that the network will be supporting hundreds of millions of transactions per day, and all fees, even if only th equivlalent of 1 cent, will be worth alot to miners.
