This new, cosmopolitan fish n chips thing would hundreds of years before it was more popular than the more traditional jellied eel n peas. I think that was the most popular takeaway supper until eel numbers started to hurt from industrial pollution.
Industrial-scale cod fishing started producing as freshwater and shore fish stocks declined. I imagine the batter's job was to mask the "weird" texture and flavour.
These days, picky eaters in the UK will only eat cod (or stuff dubiously labeled cod). No freshwater fish that isn't a trout is considered edible in the UK, even though Americans and Europeans eat pike, eel, perch, etc.
Anyway, preferences and availability always play on each other over time. Kalamari n' chips works for me. Make mine sweet potato please.