Consider a world without GINA/other regulations and with simple actuarial pricing of insurance. Say you have a 1 in 100,000 risk of a disease costing $10k before a genetic test. After the genetic test, you risk is either 1 in 1,000,000 (if negative) or 1 in 10,000 (if positive). The insurance company would charge you $1.10 for a policy if untested, $11 for a policy if tested positive, and $0.11 for a policy if tested negative. These policies result in a 10% profit per person (ignoring admin costs, etc). If you lie about getting tested, that's grounds to revoke your policy.
As a result of GINA, people can get tested but the insurance company can't price insurance accordingly. As a result, the people with a negative test will drop coverage while people with a positive result will buy it, and prices will have to go up. If everyone behaved this way, then P(disease|buys insurance) = 1/10,000 in spite of the fact that P(disease)=1/100,000. Prices will rise to $11.
Price increases will reduce the quantity purchased (resulting in lower profits) and result in political/regulatory pushback.