why does some VIP emails get sent to JUNK?

Because Apple refuses to fix their glitches. They'd rather rake customers through a long, drawn out "try doing this" resolutions, which rarely work and only further frustrates their customers. I have contacts set up that I've designated as "VIP" and they continue to go to junk. It's absurd that Apple won't fix this.

Refer to Restore the default criteria for identifying junk mail in Change Junk Mail settings in Mail on Mac - Apple Support:

"Use this option only if Mail no longer handles junk mail as you expect. Resetting the filter deletes everything that Mail has learned from you about junk mail."

I suggest you reset junk mail filters and start over. Somehow, mail junk filters are detecting an element that makes them junk.

Mail > Settings > Junk Tab > reset.

What do you mean "not even selected"? Selecting it is a manual operation you perform.