Audiobooks, like so many elements of publishing (and the world in general) have changed greatly in recent years. Once upon a time, only huge bestselling mainstream books had audio editions. They were really expensive and libraries were the primary market. (In those days a lot of audiobooks were on cassettes! Remember them? <G>)
But there was interest in audio, so gradually more genre books like romance began to be recorded. My first audiobook was The Wild Child, which came out in 1999. I was so excited–I felt that I had arrived!
I don't know if at that time any authors were producing independent audio version of their books–probably not. The norm was for the print publisher to subcontract audio rights to a specialist audio producer. The production company chose the narrator and did the engineering and distribution. (I never had any input on any of that, but I was happy that the audiobooks were available for those who wanted them.)