You're only getting half of this. Firstly half the people could be official resellers. https://mspartner.microsoft.com/en/hk/pages/licensing/Become-a-licensing-reseller.aspx#WorkWithAdistributor
My friend is, he buys a large bulk of Keys then is able to resell them to wholesalers, and retailers. But with his license he can also get personal copies.
That is where the US laws come into place. This is the part that isn't work explaining to you because you're too daft to understand.
You as a person can buy something and resell it. New or used. Magic the Gathering even tried to ban people for Buying boxes and reselling packs. (which that part is technically illegal because you're breaking apart a product and making profit on it.) But there are so many weird laws because you can get fined for selling packs alone without wizards permission, yet you're fine selling individual cards out of the packs calling them collector's items. There are so many tiny laws in and out. As much as magic says it's not okay to re-sell their products without their permission, federal laws protect us when we want to sell their products (so even selling packs alone without any licensing won't cause any discourse). Same goes for Microsoft. As much as they tell us no, if you live in the US you can resell their keys as long as you follow your state laws for reselling products.
without the software.
Key words there. When you purchase a key from a reseller all they need to do is give you a link and you have the software, it's free to download.
Those keys are either blocked as abused keys by Microsoft or will be blocked in a few weeks to a few months.
The keys my friend is reselling have never been blocked. I setup 70 computers a year ago for a company using those keys and none have had any issues.
MSDN subscriptions are only offered per individual, there are no “team” subscriptions or sharing of subscription benefits
Yeah this was a scam that went on a while back where someone was selling their key to be used to numerous people, they fixed this before windows 8. The keys are on a bulk discount not a sharing discount.
If you want to know why we are able to resell things, look toward US laws before looking towards company policy.