It's often a question of how deep your foundations needs to be dug. If the ground you're building on, or the construction technique you're using, requires you to dig deep enough anyway, then it's cost effective to put a cellar or basement in that space while you're at it - foundations don't take up the full square footage of a building, they're more like concrete walls sunk into the ground that the rest of the house is balanced on top of, so the space between those walls can be used as extra underground living space.

But most new build houses don't need foundations that deep. The minimum required depth to be below the frostline in the UK is only 450mm, so you're only digging deeper than that if you're building on soft or unlevel terrain. To be comfortable, a habitable room needs a ceiling height of around 2.2m, so if you're not already digging deep enough when putting in the foundations, it generally isn't worth digging deeper just to put in a cellar, because it's extra cost to excavate and sink deeper foundations.

This is why basements are more common in houses in colder climates, where you need to dig much deeper to have your foundations below the frostline, such as northern US states, Canada and some northern European countries.

Modern building regulations will also require basements to be properly waterproofed, have windows and adequate ventilation, alternative fire escape routes etc. which are obviously all much more difficult with an underground space, so it generally just isn't worth it.