I think you're a little confused about causality. All healthcare systems, including fully socialized ones, perform similar types of case review to ration care and hold down costs. US healthcare costs might be high now but would be even higher if the payers (including the Medicare / Medicaid government payers) paid every claim that came in without denying those that fail to mean plan coverage rules.

If we want to hold down costs then we'll have to put a greater focus on preventative care, stop expensive treatments for terminal patients, impose price controls on providers, and stop subsidizing drug development for the rest of the world. None of those measures are politically popular.