Why did they use limestone to build shelters long ago?

Answer 1

If they lived in an area with lots of limestone in, it was probably the best thing available.

Limestone is not as difficult to cut or to carve as many other types of rock, so it is relatively easy to make into blocks handy for building, and to decorate with carving, even using simple tools.

It lasts a long time, too, (although limestone carvings do eventually erode). The pyramids are made of limestone, and they've been standing for a few thousand years.

The main disadvantage is that it's very heavy.