@MrLotU What else does the help property do in Prometheus' context?
My assumption is thus:
In the application choosing to use Prometheus, and they want to make use of the help property - they will work in a PrometheusMetrics "context", where they are using more concrete types in functions, properties, etc. rather than the high level Metrics context.
However, in some low-level shared library, such as NIORedis, metrics can be provided if a Metrics object is provided. At that level, it might not be as necessary to have the help property, and the trade-off of losing that property over having metrics at all for the layer is probably worth it.
However, I could be missing what some of these types of properties, like help that you mentioned, ultimately do for each framework / service.
EDIT: Cleaned up how thoughts were expressed to be clearer.