It doesn't make sense for the Army to be in the business of developing software. They should be outsourcing this, and having a well-known vendor like SAP means there's a lot of different avenues to get bids to lower prices.
It does not make sense for Amazon to run there own shipping fleet... until it does.
The other point is that armed forces tend to have a mandate to control the supply chain, this might be a case of that.
The Army isn't a business and should never be run as one.