Beijing's fishing fleet is not just a commercial operation. It is a party-political one. It is organised as a militia. Key factory ships have Communist Party commissars watching over the captains and their operations. https://www.nzherald.co.nz/world/chinas-fishing-fleet-heading-for-australia-amid-trade-war/S5DVWRRFTB2IPAYSB3S3KWHFLI/
Selected crews are trained to work in concert with the People's Liberation Army Navy. In return, Beijing pays its fuel bill – the fishing fleet's single greatest expense. It's a massive subsidy that allows it to undercut its international competitors significantly.
Some vessels do no fishing at all. Instead, their job is to monitor the active fleet, intimidate fishers of other nations, or simply sit provocatively inside another nation's territory. This makes them a diplomatic weapon, part of Beijing's determination to wage "hybrid war".