Because they are the most versatile vehicle on the road, if you are not constrained artificially by narrow roads and heavily taxed fuel.
The biggest reason is probably purchase price. An F150 Raptor (the only model I could find a price for) is $100k in Britain, versus $60k in the US.
You do see quite a few pickups in Europe, especially as commercial vehicles. But the Toyota Hilux, Mitsubishi L200, VW Amarok etc. outnumber the American trucks at least 10:1.
And very few trucks are owned by "regular" people. Much better to get a Land Rover Discovery or a Toyota LandCruiser, and throw the big unwieldy stuff you need to move in a trailer.
(As an aside, we used to have a Chevy Avalanche with the 8.1L Vortec. That was a fun car, I'll agree, but you had to close your eyes while filling up with petrol.)
Then you have pay the yearly $675 green tax and $1.51 per litre of diesel.
I would say that taxes are constraining how many people are buying this type of car.
Edit: more taxes.
My point is that a truck is arguably the most versatile, not that it is the best choice for all use cases.
A similar cultural thing made wagons not cool in the US 30 years ago, and they didn't come back (Which is a shame).
https://www.marketwatch.com/story/how-to-make-a-tax-saving-d...
What I don't care for are the SUV designs that have basically recreated the minivan with 3 seat rows and they're really not as good for hauling people as a minivan is.