If premiums are subsidized, did the government ever think about “who” will pay the copay? The “insured” will just claim he/she has no money and walk away. Good luck with that. That’s why Medicaid nationwide is such a screaming success and healthcare for free is going broke.
The copay is the least of it. With $5000 or even $12,000 deductibles, the insurance company doesn't pay anything to the hospital or doctor until the patient owes or pays the deductible. How many people getting one of the subsidized premiums have 5 or even 10 thousand dollars available to them immediately? The healthcare providers are taking a huge credit risk.
Meanwhile, the unsubsidized family paying $1500 per month in premiums has less ability to save up the 5 or 10 thousand dollars they will need to cover their deductible and keep paying the premium. The most likely scenario is that as soon as the first $1000 medical bill arrives the family stops paying the premium and diverts that money to the hospital. Since you haven't crossed the deductible threshold yet, paying what you do owe is smarter than paying for coverage for what you might owe later - particularly if you are near the end of the year and can re-enroll next year.