Probably after the WannaCry shitshow people stopped trying to hang on to legacy exploitable Operating Systems.
Also a browser that is years behind current has a trail of breadcrumbs in terms of fixed bugs for newer versions. It is probably nearly as bad as the built-in option.
Correct. Those versions of Windows will not bet getting any crucial or critical updates.
You're better off trying to see if ReactOS / FreeDOS will run the damn thing.