You used the magic word, “modern.”

Lots of houses in this world are not modern, and some of them are old enough that they were retrofitted to have electricity, as mine was, rather than even being built with it to begin with. And done so in a haphazard manner when electrical codes were either much more lax than now or didn’t exist. And further when the expected power draw for a household was considerably lower, because basically all of it in the 1920’s or whatever was only used for lighting and we didn’t have all of our current appliances, TV’s, computers, 3D printers, or even indoor space heaters.

So moaning about what ought to be rather than what is really doesn’t accomplish anything, especially in OP’s case.

My small house has basically the entire ground floor wired to only two 15 amp circuits.