Why not? In some sense they are comparable to the cheap one-piece rubber shoes that have become available recently.
For construction workers, wooden shoes offered more protection to the foot than modern steel-toed boots. They are also perfect for working on wet or thorny ground, are relatively light, and are easy to disinfect. Perhaps most importantly, they are very durable and can be made with a skillset quite different to the one needed for making leather shoes, so for many farmers they must have been cheaper.
Apparently they need some getting used to because the muscles of the feet are more active in them. But after a while they get pretty comfortable.
The first meaning (lump) is the same in German, and I checked that yes, in Dutch you can also say, for example, een klomp goud for a lump of gold.
I hope a native Dutch speaker will comment on the wooden meaning. It doesn't exist in German and I couldn't find it in my Dutch dictionary. Clumsy seems a straightforward derivation from the lump meaning, though.