Simple Answer: The insurance company does not want to pay for proper medical care.
The Labor Code (which controls workers compensation) provides for medical care to "cure or relieve" from the effects of the injury. However, powerful special interests (insurance companies and large employers) have "reformed" the law so that you only get to go to "their" doctors. You do not decide. They do. That might work if their interest was in getting injured workers treated and returned to work instead of trying so hard to make a profit.
Even if "their doctor" requests treatment, the claims adjuster puts it through Utilization Review. This is where a different insurance company doctor comes up with a reason why the treatment is to be denied. You don't like that? Then you can apply for something called "Independent Review." (We call it anonymous review). Your treatment denial is sent to an outside company called "Maximus" that is paid by the carriers to review the denial. We are not even allowed to know who these doctors are or to even know if they are doctors.
The overwhelming member of appeals are denied. WHAT A SURPRISE!
This current system is totally rigged against injured workers. That is the way they want it. You need to let your elected representatives know that you think this is unfair and immoral.