the whole idea of insurance is to protect those who don't wait for a pre existing condition. Eliminate that restriction and you destroy the very concept of insurance. Why should I buy insurance when my ship is still floating? If it starts leaking I'll buy some insurance.
Ship to shore: Ah, it looks like we may need a little of that insurance after all.
How about families with a wife who is pregnant. Should you not be allowed to change jobs because the insurance in your new job will not cover the pre-existing condition (this happened to me in the past)? Should you not be allowed to leave your job and go independent if your wife is pregnant because the ACA individual policies will not cover your family?