I suggest it’s more to do with property developers making houses more affordable by giving them less land. You can buy houses with enough space for many cars. The reason people buy the houses they do is because it’s what they can afford. And what they can afford is a house with the amount of land that they get. If they want more land they need to pay more money.
Somewhat related, but one thing I see a lot with modern developments is detached and semi detached houses with maybe a 3 foot gap to the neighbour. Surely it would make far more sense to join them together into a terrace giving bigger houses for the same land area, and also using fewer bricks thus making them cheaper. Insulation would better too.
Are people really willing to pay more for the snob value of detatched even at the expense of less house?
Accept it might appeal if it's in the middle of a big plot or whatever, but crazy just to have 3 foot gap. You could maybe stick an extra floor on for the same cost of terraced