1. Assembly coding within a REPL. Forth supports "load-and-store" without the additional bookkeeping steps of assembly. Once the program works, it can be incrementally rewritten into the assembly if needed, or used to bootstrap something else. Historically this is probably the single biggest usage, because the language works as a blunt instrument for that within the standard wordsets. Lots of programs on the early micros shipped with code that was developed with Forth, but with the Forth interpreter discarded at the last step; and where there is novel hardware and novel applications, Forth tends to come up as the bootstrap.
2. Minimal-dependencies coding. For the same reason that it's a good bootstrapping tool, Forth ends up being portable by assuming nothing. While different Forth systems are all subtly incompatible, the runtime model is small enough to wrangle into doing what you want. Stack machine VMs basically are "Forth with more sandbox and less human-readability".
3. "Big ideas" coding. The "human-readable stack machine" aspect means it's a useful substrate for language design - being programmable, you can shift the imperative interpreter model in the direction of new syntax and new general-purpose data structures, while still retaining a way to drop all the way down to assembly - the biggest downside is that this doesn't let you easily introduce existing library code, so bootstrapping from within Forth would take a long time and you would most likely get stuck on trivial string processing. But Forth as the second of a two-step process where you "compile to Forth" using something more batteries-included is actually pretty reasonable as an alternative to generating a binary or designing an original VM.
But then you play the games, and they're all so opaque. You have no idea what's going on, and the responses to your actions are so hard to grasp. But if you do figure it out, the model usually collapses into a linear, repeatable strategy and the illusion of depth disappears. You can see this happening from the start, with Gossip. Instead of noticing that his game didn't communicate and looking for points of accessibility, he plunged further forward into computer modelling. The failure is one of verisimilitude: The model is similar to a grounded truth on paper, but it's uninteresting to behold because it doesn't lead to a coherent whole. It just reflects the designer's thoughts on "this is how the world should work", which is something that can be found in any comments section.
Often, when Crawford lectured, he would go into evo-psych theories to build his claims: that is, he was confident that the answers he already accepted about the world and society were the correct ones, and the games were a matter of illustration. He was likewise confident that a shooting game would be less thoughtful than a turn-based strategy game because the moment-to-moment decisions were less complex, and the goal should be to portray completeness in the details.
I think he's aware of some of this, but he's a stubborn guy.