Why many companies are not using WMS? How they can pretend to manage efficiency the stock and transactions?

My last employer (an FMCG distributor) with2 warehouses, each with more than100K Sq Ft area (Food and Non-food), more than5000 SKUs is still not on WMS though they have SAP for the last12 years!!!

Yeah, We can manage with out WMS, But to maintain Stock Accuracy, there is an alternative method, where we will maintain BAY NO: & BIN CARD NO: & QTY in an excell sheet which is also called as IMF( Inventory Management File) and have to keep on update the master file.In practical it is possible and we successfully implemented and now it is existing.