The missing link here is premium savings. HDHP plans exchange higher deductibles for a nontrivial premium discount. Insurance companies like to assure employers that employees will bank this discount into a tax-advantaged HSA. So the theory goes, a reasonably healthy subscriber will have sufficient savings to meet their deductible.

This falls apart in practice when employees, who are already spread thin financially, elect an HDHP but can't or won't set aside cash to cover expenses.