You won't get stack traces for functionality that is disabled by
default and mostly useful to beginners.
The people that would be able to send useful reports and debug the
problem are not the kind of people who would think it useful enough to
enable it. And those who would benefit from it usually don't have
enough skills or knowledge to actually enable it themselves.
Enable it by default, and you'll get the reports. And if you don't
get any, the change presumably was good.
Just for fun I tried turning on balloon-help-mode in
21.4.19 native Windows, and whilst it's decidely sub-optimal [1], I haven't gotten it to crash yet. I'll leave it on for a while and see what happens.
Robert
[1] It creates an invisible dummy frame to act as the parent of the ballon-help window, however that frame does not stay invisible, nor can it be deleted. Oh, and the window containing the text is too small, maybe by 1 character.