Why do some elements exist but not interactable/displayed?

I'm pretty new to testing, trying to gain a better understanding of what exactly is going on. I'm finding some of our test codes are failing when the css selector element has a waitUntilCanInteract or waitUntilDisplayed attached to it even though when I do a chrome inspect the element is showing up in the browser. Changing them to a waitUntilExists gets them to a passing point so I was wondering what exactly is going on to create this situation?