Bottom line, there are people all year round who become eligible for Medicare for one reason or another.
This^
Free, Free, Free...you qualify for everything FREE!
And unfortunately some folks call and get talked into stuff for big $$
The Medicare stuff so frequently advertised on TV are for the "Advantage" plans, and are "free" in that they usually don't have a monthly payment you have to make. Instead, you get hit with pre-pay fees, larger out of pocket costs, and limited choices of where you can get treatment when you have to see a doctor. They are basically HMO's, and are administered by the organization and not Medicare.
So, you have a choice: pay a monthly billing for your Part B supplement, whether you need a doctor or not, and when you do see one, there's no co-pay or out of pocket expense beyond paying what the supplement doesn't. That's like your work insurance plans, where insurance pays 80% of "reasonable and customary" charges and you pay the rest, or where insurance will pay 100% in many cases, and you can go to the MD of your choice. The other side (Advantage plans), you pay nothing from month to month, which is a good deal, I suppose, if you are healthy and don't need a doctor regularly for chronic issues. But, when you do need one, you have to use someone from the list that accepts your particular Advantage plan; and there will be co-pays, up front costs for specific treatments, and higher out of pocket costs for specialty stuff like MRI or CT or E.R.
The government loves them because they will eventually privatize Medicare. My retirement planner warned me about them when I was planning my retirement a couple of years ago.
It's basically Pay $ now, or Pay $$$ later.