I think it's more a combination of vertical integration and Nvidia upper management actually wanting to provide support for so long. Apple, Google, and Samsung all make smartphones with their own chips, and yet none of them support running the newest OS on 10+ year old devices.
I have to wonder if the Nintendo Switch picking up the Tegra X1 SOC has something to do with it. There's a good chance a lot of components of the (custom microkernel) operating system are derived from Android, and with the Switch receiving active support for so long, I wouldn't be surprised if the work between the Shield TV and Switch are related.
With the Switch being shipped for nearly 10 years, it pales in comparison to the shelf life of most any processor Apple, Google, Samsung, Qualcomm, MediaTek (?) push out.
Though Apple in particular is interesting, as their Apple TV lineup also has the same long legs, with the Apple TV HD/4th Gen releasing in 2015 and receiving the latest OS.