Bed springs are alternative to the traditional mattresses that contain all kinds of fibers: cotton, wool, hair (horse hair, etc), feathers, hay, kapok, sea grass, etc. In fact, Bed springs are better than any natural fillings for support because these natural fillings compress quickly, some fillings shift. Tufting is a technique to fix the issue of shifting fibers. Pure wool/cotton mattresses need to be opened every year, and re-teased. Good springs (open coil or pocketed coils) are far better than any wool/cotton/hay support.

The modern mattress industry undermined this durability in pursuit of quick profit: springs became thinner and cheaper, and comfort layers were replaced with low-quality foams. That’s why today’s mattresses don’t last the way they used to.

I believe the OP is talking about "Box springs", not spring mattresses. These are boxes that make the bed go higher, and are required for certain types of frames.