It's just that the time and money to convert the bike would be wasted versus just buying the "right" bike to begin with. The Moab has suspension-ready geometry, you would need to find a rigid fork with the same geometry. Then you need a new stem, bar, brake levers, bar-end shifters, a full cable kit, and bar tape. Unless you have an extensive parts bin or incredible patience to track down used parts, it just isn't worth it.