Some insurance companies don't cover the cost of treatment for a disease that you had before getting your insurance. Why do they do this?

Lets assume, I have an injury in my hand and it needs 3months medication to recover. I'm going to take a policy means they will exclude the hand injury services for 3months since the overall insurance profit depends on the probability of the incident vs the revenue they make from the members.

Yes this is true to avoid adverse selection, think on car accident, it is not logic to ask for insurance licence after car accident, no insurance company will accept this

That is because the insurance concept based on the mechanism of covering and accepting unforeseen incidents at the time when insurance contract is approved by insurer . If the loss was already occurred at the inception of the insurance policy the insurance company does not accept this unless the insured accept that the insurance company premium charged against his insured property is  equal to the total sum insured , which is impossible'

I hope that my point in this issue is clear.

Thanks .

Varies in different countries according to regulations, No insurance companies can charge the same rate that they offered for healthy insured member.

Obviously the costs are too high to manage such members with preexisting conditions.

Further, the life threatening preexisting are covered in Saudi Arabia as per the guide lines of Cooperative Council Of Health Insurance (CCHI). However, for corporate policies one can negotiate with the underwriter and keep a cap to cover the non life threatening preexisting conditions to be covered for certain limits.