Each item may have multiple suppliers. When purchase orders are raised the item is included for each supplier.
It would be great to have an option to select a default supplier (or active supplier) for a particular item so that that item is ordered from the default supplier only.
Also in the bulk csv upload, instead, or in addition to last supplier, it should have default supplier & their supplierSKU
Just because you change a supplier because of, say, out of stocks, it doesn't mean that you'll continue to use them.
You almost always use your default supplier, that's pretty standard.
But make it that you can still purchase a product from a different supplier if you need to