Canada

You are correct they do exist in small quantities, and they do cost more then a single family home.

The reason the cost is higher is because apartment designs with a single long corridor down the middle cause a 3 or 4 bedroom coming off that corridor to usually have 200~300 sq foot more then needed in the layout/design.

Compared to a point access layout for example where layouts can be arranged in a multitude of ways and layouts can become more efficient in use of space.

This article here demonstrates these layouts a little better then I can, it also shows how the sq footages increases as more bedrooma are added along the single corridor layout.

https://www.centerforbuilding.org/blog/we-we-cant-build-family-sized-apartments-in-north-america

So all these factors essential drive a choice of either living in the suburbs in a single family home, or a 1 or 2 bedroom large condo towers in a city center.

The trouble with this is we are "missing the middle" housing as shown in these videos. Homes for growing families that don't want to live in the suburbs and don't or can't fit into a two bedroom apartment tower, or can't afford the 4 bedroom condo layout. Or families that don't want to stick their kid into a den without a window.

We need homes such a 4 plexes, 3-4 level condos, laneway homes, all the layouts that are essentially illegal in north america to build.