The invasion of Ukraine drained the U.S. stockpile of 155 mm shells and those of European allies leaving them unprepared to support a major and ongoing conventional land war.
Exactly where at we at risk of a "major and ongoing land war", other than the one already taking place in Ukraine?
Russia trying to rebuild the Soviet Union is pretty much the only major land war that was ever on the table. I suppose the other option is South Korea, but the ROK's we're always going to carry the vast majority of the workload on land in that war, and they have plenty of wat stocks.