Why Are Older iOS/MacOS' Still Not Available?

I can't speak for Apple as to the "why?", but rather than try to download old macOS versions at the App Store directly, you can use the installer download links found in this Apple document:

How to download and install macOS - Apple Support

As long as an older Mac is operational, these can be used when the "Software Update" path doesn't work.

These are also the downloads needed when trying to create a bootable USB installer.

broncojoe wrote:

I have come across a number of Mac users who may not be the most tech savvy. They believe that their Macs are always up-to-date with the latest iOS, but when I look, most of them never updated past Big Sur up to Sierra or High Sierra. When I try to see if I can get them updated to Sonoma or Sequoia it is not an option since I cannot get them updated past Sierra. When I go to the App Store there is nothing that can be done. I have found locations where there may be a chance download a copy of Sierra.

Why does Apple not allow a process to let users who were unaware that their Macs never updated to be able to update? I understand some laptops a too old and maybe not powerful enough to support the higher MacOS', if that is the reason.

Would like to know when I have people ask me why they cannot do it.

Any Mac that can run macOS 10.12 can run macOS 10.13. That is all, however, nearly a decade out of date.

First, some terminology: macOS updates can be configured to install automatically as they become available, but upgrades are not.

macOS updates are intended not to disrupt existing installed apps, while macOS upgrades can break existing apps.

Automatically upgrading a Mac to macOS 10.15 for instance, would likely create a firestorm of users with now-broken 32-bit apps.

Apple does provide information on new macOS versions, but those notices routinely get ignored.

Apple is seeking to address some of this confusion with the “26” version numbering coming into use later this year as well, so the displayed versions are no longer cryptic version numbers, or the spectacularly cryptic release names. Somewhat less cryptically than macOS 10.13, or macOS 13, etc., macOS 26 is the version number for operating system releases during 2026. In addition to macOS, iOS, iPadOS, and such will be following the same “26” pattern, too.

Adding to the general complexity and opportunities for confusion here, older Mac hardware also ages out, and newer versions of apps and newer web services can require newer macOS versions. And newer or new Mac hardware.

More than a few Macs are running the final supported version for the particular hardware, and will do so until the user encounters some app or service block requiring replacement with a newer or new Mac. I’m still working with a few end-of-the-line “stuck” Macs in various places, and the owners of those are slowly working to replace the apps and services involved.

But if you can figure out some way that all works better, do let Apple know.

Only Apple can decide a particular product's eligibility to update its operating system, but those reasons generally involve hardware limitations that cannot be overcome. Newer operating systems with newer software offering commensurately newer features requires newer hardware.

So why don't people upgrade? Not everyone needs those new features, or consider it worthwhile to spend a thousand dollars or more every couple of years just to have the latest best thing.

There in nothing wrong with older Macs, but even Big Sur is not new enough for a lot of software.

By the way any Mac that can run Sierra can run High Sierra. There are no disadvantages to that specific macOS upgrade.

That doesn't change the fact that even High Sierra is woefully outdated at this point.

Re: “They believe that their Macs are always up-to-date with the latest iOS”

Macs don’t run iOS. They run macOS. The desktop operating system macOS shares much code and technology with the mobile operating systems iOS and iPadOS, but there are also many significant differences.