There has always been ready made terrain. Nowadays there is a much wider variety available.
You can even get space corridors! And lots of useful add on parts for enhancing homemade pieces.
I still like to make my own stuff with the help of bought stuff. In this pic the cloth and hills are bought in. The alien cactus forests are bought resin pieces on top of sandpaper. The various buildings are things like Japanese soup bowls and yoghurt containers enhanced with detailing pieces various sources.