This happens all the time when people switch insurance or go onto COBRA. You get retroactively covered for some period after your new plan becomes active.
It doesn't end up with people paying tens of thousands out of pocket, people just don't pay the bills that come in during that period, and kick them to insurance later. It sucks but is not really uncommon or possibly even something Intuit has a ton of control over.
COBRA wasn't that far off of marketplace prices for me. If I thought I'd use the better coverage/better benefits during the COBRA period, and I was confident my former employer would inform COBRA users of issues at least as well as they did employees, I might have considered it.
IIUC, COBRA rates are more or less the total employee and employer rate, maybe plus a limited administration fee? Also, I don't think COBRA pricing varies by age, but marketplace plans do, so if my spouse or I were older, COBRA might have been a good deal.
All that said, I think most people switching jobs keep the COBRA paperwork in case something big happens before they get new coverage in place. There's a grace period on the first payment, if you need coverage, you can pay until the grace period and get retroactive coverage; if you don't need coverage, don't pay. Some people even prepare the payment but leave instructions to send it in if they're incapacitated.
It doesn't end up with people paying tens of thousands out of pocket, people just don't pay the bills that come in during that period, and kick them to insurance later. It sucks but is not really uncommon or possibly even something Intuit has a ton of control over.