When I was watching Young Justice on HBO Max back in March, there was a running gag throughout the show from the first episode. Dick Grayson, aka Robin and then Nightwing, questions why we say we're "overwhelmed" or "underwhelmed," but no one ever just says they're whelmed. And it's like that with a lot of words. Another one they use in the show is "disaster." No one ever uses the root word "aster" by itself, do they? Another one from the 3rd season is "distraught." Have you ever been traught?
Other words we might use certain conjugations of the word but not the root word itself. Like you call someone a "burglar" or you might say there was a "burglary" last night. Sometimes they might even say a house was "burgled." But no one would say, "Let's burgle that house."
Another instance is that you might get REvenge or Avenge something. You might be vengeFUL or act vengeFULLY but venge by itself is not a word we use.
Or you could INTERcept something. Or you might try your hand at INceptION. You might ACcept something. Or EXcept something or make an EXceptION. But cept isn't really a word on its own.
Or you may REquire something and you may ACquire something or even REACquire something but you don't quire anything, do you?
In a lot of cases it's probably that long, long ago people did use the root form for something, but over time it fell out of favor. Instead of saying I'm "whelmed." people say they're "fine" or "OK" or something like that. Hence it becomes less and less common until it all but disappears. "Disappears" does not fall into that category because we do use "appears" still. But "instead" is used probably a lot more than "stead" on its own.
I'm sure you can think of more words that fall into these categories. Maybe I inadvertently (or not) used some in this post. Like "inadvertently." How often do you "vertently" do something?