It's used by a lot of enterprise software -- like the kind that will still be running more or less unchanged a decade from now.
I find it a pain in the ass to write SOAP interfaces, but I don't mind at all working with them. Running a compiler on the WSDL file for my programming language of choice is often a lot faster to get up and running than wrapping a REST API and WADL seems not to have really taken off.
When I've developed APIs, people clamor for JSON, REST, and serialized PHP. Maybe I'm in some non-Microsoft, non-Java ghetto?