I was simply answering the question posed in the thread title as others have done since
1) fishing is a dangerous and often erratic as well as labour intensive industry, dependent on many imponderables
2) costs cover a multiplicity of elements- not least fuel for the fishing boats, as well as for distribution
3) fishermen deserve a decent wage (see 1)
4) stocks of what used to be regarded as ‘cheap’ fish can be sadly depleted due to over-fishing, fishing rights regulations and yes, rising sea temperatures due to climate change
5) tastes nationally may have changed, many shoppers prefer more exotic imported foodstuffs over the humbler coley, hake, haddock etc
6) Frozen food has made it possible to import fish from other parts of the world where wages and health and safety measures my be less well regarded.
7) with the exception of the likes of fish farms for salmon, or mussels, fish cannot be reared intensively like chicken or pork
Enough reasons?