why do people care so much about Kim Jong Un health when there are bigger things at stake like COVID-19?

I have absolutely no concern at all for Kim Jung Il,, I actually have far more concern for the health of that possum walking along the top of my fence right now than I do for that little weeble in N.K.

Perhaps you should direct this question at little Donnie John,, he seems to be more concerned with Kim Jung's health that he is with the health of the American public.

Probably because an unpredictable country in possession of nuclear weapons and long range missiles could be of concern if it becomes politically unstable.

Such as may happen when Kim Jong Un eventually dies or is deposed.

Instability in North Korea could trigger a world war involving the US and China that could kill far more people than the virus. 

It's possible to have an interest in more than one thing, believe it or not.

It’s like watching a horrible car accident. Dead bodies draw eyeballs 👁 

No one cares, that's the point.