If they truly wanted to stop this practice they would set up strict distribution agreements and enforce them.
That is EXACTLY why you see grey market products!
One countries distributor is responsible for that countries distribution AND warranties.
When a BUYER goes to a distributor in a third world country and buys 1000 copies of a camera, that distributor can allow for a sizeable discount on the volume sale. Its even EASIER for that distributor to discount the sale when they know they will never have to warranty and of the product failures because they know those items will be shipped overseas.
That volume buyer then puts the items in a cargo container, ships them to the country he is intending to sell them in, and sells them below market price to move them quickly and still turn a profit. The manufacturers CANNOT tell their distributors who they can or cannot sell product to as that would be in direct violation of international fair trade laws. This is a simple matter when you understand free world trade.
The authorized distributor in the country where these grey market products are sold makes no profit from those sales so they have no interest in repairing them, either under warranty or for a fee, because repairing them for a fee would bolster and increase grey market sellers, not reduce them.
Nikon Sigma, Tamron, Sony, Pentax, Olympus, and many others refuse to work on grey market products at all. Canon says is "MAY NOT" work on grey market items, even for a fee, and I have personally had repairs denied by Canon because of grey market customers gear I have sent them. I did get one camera body repaired by Canon that was grey market, but it was a brand new 5D III that a customer had installed an EF-S lens on and ruined the mirror box. The repair cost the customer $585 plus shipping both ways.
The only winner of grey market sales is the unauthorized importers. The manufacturers are losers due to the bad reputation the practice causes. The BIG losers are the consumers who buy this stuff not knowing it is grey market, or not understanding the repercussions of buying grey market.
The whole point of these discussions is to inform the consumer of those repercussions and risks. Information is power, use it and don't make costly mistakes buying grey market. Or if you do buy grey market, don't waste everyones time by snivveling about it, that will never get you anywhere.