It's not actually about the fishermen, it's about the whole rural communities.
Just like farming, it's everyone living out there. How the fishers and farmers are being treated is how those communities at large feel like they're being treated. And they always feel like they're being shafted, even though that's just progress and other industries got shafted much worse in the past.
So for every 1 fisherman, there are 20 other votes. And they all generally vote conservative, those are blue strongholds (blue over here is conservative, red labour).
For every 1 Games Workshop employee, there's no other votes. Even spouses will be fairly uninvested in how the government is treating toy exports.
But on the other part of your comment, there's been no 10% GDP loss. Note, I voted remain, and would vote to rejoin in a heartbeat.
But we're roughly at the same position today in the world as we were in 2016, compared to other countries. Sitting about 6/7th in the world. Everyone's suffered since covid, everyone's struggling with growth. There's been no big drop in GDP. So it was actually scaremongering. It feels like there's a conspiracy of economists who lie, heavily influence markets, but their lies don't match reality. It's ideological propaganda for free-market capitalism, rather than fact.