@fatalogic is right, unfortunately. It's the same on the iPad line, where the larger iPad Pro has better internal hardware than the smaller Pro, and where the mini hasn't been receiving regular updates and is generally kept a generation behind the other iPads. It's also similar with the iMac line, where you need to go to the larger screen to get the best internals.
I'm with you, though. It's frustrating that Apple does this. They're a company that seems to have made portability its absolute mission, yet they treat the most portable and most accessible devices like they're an "economy" option. I went with an iPad Pro (smaller version) to upgrade my iPad mini simply because Apple wasn't updating the mini. I went with the iPhone 7 Plus over the SE when I upgraded my iPhone 5S mostly for the camera; admittedly, the SE is a pretty nice phone, but it remains to be seen if Apple will continue to update it or even keep it around. I'd gladly pay more for an updated iPad mini or an iPhone SE-like device if they had feature parity with the larger devices in their lines.
I'm with you, though. It's frustrating that Apple does this. They're a company that seems to have made portability its absolute mission, yet they treat the most portable and most accessible devices like they're an "economy" option. I went with an iPad Pro (smaller version) to upgrade my iPad mini simply because Apple wasn't updating the mini. I went with the iPhone 7 Plus over the SE when I upgraded my iPhone 5S mostly for the camera; admittedly, the SE is a pretty nice phone, but it remains to be seen if Apple will continue to update it or even keep it around. I'd gladly pay more for an updated iPad mini or an iPhone SE-like device if they had feature parity with the larger devices in their lines.