Samsung makes fast expensive storage but even cheap storage can max out SATA, hence there's no point Samsung trying to compete in the dwindling SATA space.
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You can buy cheap add-in cards to use PCIe slots as M.2 slots, too.
If you need even more slots, there are add-in cards with PCIe switches which allow you to install 10+ M.2 drives into a single M.2 slot.