I suppose this is maybe open to discussion, and I agree it is very harsh.
But without it, what's to stop you from doing something like;
monster : object "monster-with-a-huge-horn-and-an-angry-face";
?
Such names are not truly necessary. They can be reworked.
- six-pack could be tinnies.
- mother-in-law could be mother.
Trying to fit within the constraints of the jam will necessarily lead to things that are simply not possible. In my mind, the point of such a cruel and arbitrary constraint in the jam is to force the use of creative ways around them I suppose. It may require renaming things, or reworking characters (mother rather than mother-in-law).
The two word limit for objects, maybe could be reduced to a three word limit, but I think part of the fun of the jam is to try to fit under that limit. Hyphenated words are clearly a way to exploit the word limit. I did put in an exemption for 's, because it's a terminator and 's' by itself is a grammar modifier, not a conveyer of more information. But is mother-in-law one word or three words? Most people would say three, hyphen or no hyphen.