I am continually astonished at folks who expect OS and/or security updates past a few years (this is not a slight against you, just an observation on my part)
A lot of folk like to gripe about "planned obsolescence" or similar because eventually their device is no longer supported
Yet the fact that manufacturers support equipment as long as they do is ... kind of astonishing
The higher the volume of production, the shorter you would expect a manufacturer to support it (a 747 is worlds different from a pickup truck which is worlds different from a phone or laptop)
The cost-benefit analysis of continuing to support/update a given device has to be taken into account ... and - for most phones (since that is what we are talking about in this thread) for most people, that means that between 3 and 4 years after release, it makes [nearly] no economic sense to keep supporting them
That Apple does for so long speaks volumes about their commitment to their customers (even though, of course, they would like you to get a new phone every year, I am sure)