During my intro to computer engineering course, lectures touched on why NAND gates, and the conclusion was that you can build anything you need in a basic computer using NAND gates. It boils down to expense. A BOM (bill of materials) with fewer line items tends to be cheaper.
This doesn't really hold in today's world of silicon prints, but at the start I think it was price that drove the decision.
Actually if you take an XOR gate with a naive translation into NAND gates you would use 20 transistors, but if you don't need a large fan out from the output you can actually do it with 6 transistors using a pass gate layout (which is neither NAND nor NOR). So typically you don't use NAND vs NOR because of transistor count.
This doesn't really hold in today's world of silicon prints, but at the start I think it was price that drove the decision.