How many people own a microwave though? Most people i know don't have one and would rather spend to money on getting a proper oven.
Microwaves also seem like they have little use compared to things like a stove or oven. Atleast i personally have barely used a microwave when cooking.
This is not the reality I live in. Everyone has a microwave, and for people in student halls or less affluent accomodation, it's sometimes the only available way to cook. For many (in the UK) 'ready-meals', most of which are preparable with just a microwave, are a staple part of people's diet - even among more affluent, but time-poor people. There's usually a whole supermarket aisle dedicated to these foods.
Individual accounts are of course often of modest value, however, I've literally never known a person that didn't have a microwave in their home, rich or poor, in the US. It's one of the things that is nearly universal in homes.
They're too inexpensive to not buy due to cost, and they're too useful (even if only used in rare circumstances) to disregard as a part of a kitchen. They take up a small amount of space, and come in numerous sizes to fit spacing requirements.
Essentially every supermarket in the US also has a frozen meals (ready-meals as you say), or equivalent, aisle. The items in those aisles appeal to just about every price point these days. They're clearly still quite popular.
Microwaves also seem like they have little use compared to things like a stove or oven. Atleast i personally have barely used a microwave when cooking.