Transaction fees are less than 3% of the total revenue in the bitcoin mining industry

Bitcoin miners have generated $5.26 billion in revenue in 2018 — $4.98 billion from block subsidies and $284 million from transaction fees. This year, miners have so far generated $4.30 billion — $4.15 billion from subsidy and $146 million from fees. The revenue was estimated under the assumption that miners sell their bitcoins immediately, which is not exactly accurate as some companies retain a portion of their mined BTC to sell at a later date.

To put things in perspective, Barrick Gold, the largest gold mining company in the world, produced 128.3 tonnes of gold in 2018 and generated revenue of $7.24 billion. The global gold mine production was reportedly 3,332 tonnes in 2018 meaning that the total revenue generated from mining gold was likely upwards of $150 billion in 2018. That would make gold production at least a 30 times larger industry than Bitcoin mining.