I hate to admit it, but this stuff just does not move
I get what you are saying KC, but in this instance, it is an 18" front rim and even if the part number was known, the demand for an 18" rim versus the more popular and most widely used 19" rim is very limited. Hence, the chances that a member here who is looking for or needs this rim is already slim.
With that said, there are a host of reasons to keep it listed.
1. It doesn't cost anything.
2. Maybe the person who needs it, hasn't seen it yet?
3. Maybe another member acquires a bike that needs this rim
4. Someone decides they want an 18" rim up front and boom...you are there to meet the need.
I could probably find a few more but you get the idea, I'm sure.