I don't believe it was due to loosing popularity.
IIRC it was to keep the weight the same for bullseye shooters.
Where a k22 and k38 would weigh the same.
I think very early 1920's as I don't see the made in USA stamping.
It's a target version so value is more than a fixed sighted one.
Exactly what that is I can't answer appropriately.
I'd love to have that gun.
A 32-20 target has fun written all over it.