Why insulate the walls rather than the floor joists in a crawlspace?
...age about crawlspace insulation, that may answer your questions-
The best way to insulate a crawlspace
When you’ve seen crawlspaces with walls insulated and not the floor above, that will keep the crawlspace warmer. When there is insulation between the joists, that will slow heat from above, so the crawlspace will be c...