There can be a lot of reasons but a common one is return to vendor/manufacturer agreement or a sale or return agreement, often when a brand wants to maintain a certain price point or to minimise risk for themselves and the retailer, etc. they'll agree to buy back a certain amount or guarantee a certain number of sales or they will buy back the unsold stock and/or the retailer doesn't pay for the stock until it sells or returns it if it doesn't - at which point it will generally be offered to another retailer, etc.
One I've seen a bit over the pandemic - a business will buy say 200 printers for people working from home sourcing the same model from several different retailers - then return say 20 of them and not bother themselves too much as to which was bought from where just the quantities going back to each.
It isn't entirely unusual for a company to buy the same product from another company when they've run out of stock, etc. and have them send it to the customer rather than lose a sale, especially if someone has bought a load of stuff on the same order.
