Since iOS 8, older iPad models such as the iPad 2, 3, 4 and the original iPad Mini have only been getting the most basic of iOS features.
They all share similar hardware architectures and a less powerful 1.0 Ghz CPU that Apple has deemed insufficiently powerful enough to even run the basic, barebones features of iOS 10. The iPad 2, 3 and 1st generation iPad Mini are all ineligible and excluded from upgrading to iOS 10.
