There are new-ish monolithic pour techniques that enable slab foundations in frost prone areas. In particular, the usage of rigid XPS insulation in the soil and maintaining a minimum temp in the structure allow more efficient foundation construction.

I grew up with a basement (in MD) and have one now (in MA). Basements seem so incredibly practical and useful that if I could have one, I’d choose one for sure.

Not disagreeing (have a finished basement myself), but what's in question here is affordability and efficiency.

In that context, a monolithic slab has a lot of benefits including reduced material that has to be removed, reduced site prep, reduced construction time, reduced material costs, reduced labor costs, and reduced complexity.

If the goal is to make more housing, more accessible economically, then it makes sense in that context.

It depends somewhat on how dry they are. Mine isn't very. But there's generally a fair bit of utility infrastructure that has to go somewhere. And even if it's not a finished basement it provides a lot of storage which is really useful if you don't have an attic.