No Bronze Guides, Any Reason?

When working on hostile environment engines we found that certain guides were incompatible with certain stem materials
same with unleaded applications
we ended up with hard chrome stems and threaded/ knurled guides
we even knurled new iron and steel guides then ream and hone)
but here we have stock guides that are worn
problem with mopars is getting a replacement guide concentric with the oem guide/ seat
hence using inserts either solid or coils