The REST API I had to forward through however had no good documentation, no client library, so I was forced to write json serializers and reverse engineer the code. Overall, when you have a well written SOAP interface (rare, admitted), development time can be greatly reduced.
I learned SOAP relatively recently, but well after it was a fad. Today, my experience would be like yours if I had to make a SOAP service with just a WSDL. But when I started out? It would take a longer for me to wrap my head around all of it. I can't imagine how confusing it would be if I had to do it all without the benefit of working on a team whose focus is a SOAP-based product. I dunno if I would know where to begin.
Compare that to REST. Even if you know next-to-nothing to start, you can do a basic REST tutorial for just about any stack in an hour, and get a basic implementation of an API up in an afternoon.
Also, you don't seem to have looked terribly hard, because there are a few really powerful tools out there for autogenerating server and client code for REST APIs, as well as mock servers and a whole host of other tooling (See: Swagger, RAML, API Blueprint for starting points).
I've used a variety of tools to generate and test REST interfaces in the last ten years. To a mixed success, I must say.