For some reason, Apple does not allow third-party developers to create dials for Apple Watch. However, this may change in the near future, if you believe the watchOS 4.3.1 code. Data from the code indicate that in the future Apple Watch will begin to support third-party dials.
Most likely, support will appear with the release of the version of the watchOS 5 system, which will be presented at the World Conference of Developers 2018 in a couple of months.
The NanoTimeKit component responsible for the dials contains developer tools for working with Xcode on a Mac . The code looks like this:
Apple likes to severely restrict its operating systems, and so the company allowed the support of third-party dials only now. However, with the release of watchOS 5 should appear a variety of different and high-quality dials for Apple Watch.
Third-party dials will allow Apple Watch owners to customize them to their taste. At the moment, Apple offers about 15 dials. This and so many, but for all this time they are probably tired of users, and a greater choice of them will only please.