It's understood that many actors who sign deals with Disney and Marvel Studios do so under the grounds that they will appear in X number of projects in the future. It's also somewhat understood that the actors are almost assigned which projects they appear within, which is what makes the lack of additional appearances from Moon Knight all the more unusual.
Ever since the character was introduced in the Disney+ series of the same name, we have been waiting for Oscar Isaac to return as Khonsu's champion, but so far nothing of substance has ever bubbled to the surface. And we seemingly now know why.
Speaking with Comicbook.com, Moon Knight creator, Jeremy Slater, has explained that Isaac somewhat holds the cards and determines when Moon Knight (or one of the many alter ego personalities) will return. Essentially, Isaac seems to be able to determine which projects he wants to pursue and appear within, hence why Moon Knight has stalled in his MCU expansion.
"The contract Oscar Isaac signed was very much like, we will do more stories when we find stories that he is creatively excited to tell. They can't just sort of snap their fingers and summon him back for another adventure. He's really creatively involved in the future of that character. So I would imagine part of the challenge, and part of the joy over there, is finding: what stories does Oscar want to explore, and how does he want that character to be used? What's something that would entice him to get back and play in that sandbox one more time?"
This suggests that we really shouldn't hold our breath on more Moon Knight, as it doesn't seem like Isaac or Marvel are too focussed in returning to the character or the wider universe, at least not in the same way as Chris Evans, Robert Downey Jr., Chris Hemsworth, Tom Holland, the list goes on.