Because MAGA ideology sees prosperity only through the lens of triumphantly screwing over others, they can't recognize mutual benefit as a victory. This shortsightedness will cost countless lives in the years ahead.
Even then, it only became a stalemate because US politicians were unwilling to risk further escalation (as in Vietnam).
PS: THAAD missiles are $12M each and GMD missiles are $75M each make for much simpler burning money rather than using it for food, housing, medications, or healthcare.