My suspicion on why it's only done by some performance gun makers is that it bucks the manufacturer standards organization specs (SAAMI, or other foreign orgs). SAAMI specs include the cone. Most of the makers you mentioned are likely SAAMI members, except maybe Galazan.

Krieghoff choose to go the long cone route a long time ago. I think someone mentioned Kolar did as well. Possibly other target gun makers have as well.