This is because the material characteristics were so important that there simply were no good alternatives. Just like you would use steel for one thing and aluminum for another today. There were whole libraries of wood samples that you could go and look at or even test to ensure that your structure held up. Windmills are another item where wood from multiple locations came together.

Wood ranges from one extreme to another in terms of density, hardness, ease of working, strength in various directions and so on. There are hardwoods that are so hard that you can't really work them with normal tools and there are softwoods so light that you have to handle them carefully or you'll dent them.