Most major brands never even touch their products. They design them and have them built by contract manufacturers. They then get sent through distributors, shippers, brokers, etc. Each of which has terribly old systems which may or may not track each individual item.
Most links in this chain are also disinterested in any third party knowing what and how many products they move, including and especially the brand itself.
I think your last paragraph is absolutely key - many players treat that information as strictly proprietary. A big reason is because oftentimes a supplier makes identical (other than the packaging) products for two different customers, one sold as generic, one name brand.
Most major brands never even touch their products. They design them and have them built by contract manufacturers. They then get sent through distributors, shippers, brokers, etc. Each of which has terribly old systems which may or may not track each individual item.
Most links in this chain are also disinterested in any third party knowing what and how many products they move, including and especially the brand itself.