To be fair to Apple, the 1st gen SE came out in 2016 with a 2015 chip and a 2012/2013 body, supporting it for this long is very impressive. There's still the later generations SE (I'm very happy with my SE2) or the 13 mini.
I do agree with you that Apple have done well to support this. But also 2016 is only 6 years ago. It's not just Apple thing, but it really doesn't feel sustainable for us to keep write off our hardware every half a decade.
I feel like expecting 6 years of updates out of the iPhone 4 would have been kind of ridiculous!