Ernie, the OP isn't having issues because they 'upgraded'. They didn't upgrade. They're just on a really old platform and now having problems finding support for it (which shouldn't come as a suprise).
I've been on every version of Mac since 10.2. Apple easily has the simplest upgrade process in the industry. There is no "perfect" platform ... but it has far fewer issues than any other platform on the market. (I can put this in contrast with Windows... where the upgrades really get ugly, result in data loss and numerous other problems. This past summer I had to completely wipe and rebuild my Windows 10 laptop due to upgrade problems.)
I have run into a few issues that were predictable. For example the industry body behind the USB standard will update that standard from time to time (e.g. USB 1.x, 2.x, 3.x, etc.) and now we're up to "USB C". Each time this happens, the OS vendor has to re-write the USB stack. So I've seen instances where they don't bother to port drivers from ancient USB devices to run on the latest stack (for example, I had a "USB" attached modem, but as nobody uses dial-up modems anymore, they didn't bother to port the driver so the device no longer works.) Microsoft doesn't allow mixing 32-bit drivers in a 64-bit OS (and that's understandable) ... so users with very old devices that didn't offer 64-bit drivers didn't work. But it makes sense as to why those situations happen.
On the mac, upgrades are really pretty painless. Also they are free. So there's no good reason not to do it.
It costs money to support old platforms. Most companies support the "current" OS and maybe one or two older releases. But it's not worthwhile to go back too far and trying to do so comes with a lot of problems. This would result in higher costs ... which they'd have to pass along to the consumer (usually by selling products at higher prices).
Another issue has to do with staffing. Nobody wants to be the developer or support person stuck on the old out-dated software. For career reasons... you want to work on the "new" stuff, not the "old" stuff. Consequently, it is actually HARD to find people willing to do that job (and if you force someone into that job and don't get a plant to migrate them out of the role, they update their resume to find a job at another company). These are the realities of the computer industry.
There are security issues as well... since software updates stop happening for out-of-date platforms, when security holes are uncovered, they are not patched. You really want to keep current on security patches and that means you want to be running on a "currently supported" OS version (it doesn't have to be the latest platform, but it does have to be new enough that it still gets updates & patches).
In the industry we sometimes call this situation "technical debt". This is when a person lets their technology fall so far behind that its age is causing problems because it isn't really supportable. When they eventually have a support incident... there's no simple way to resolve it and they basically HAVE to upgrade (even if upgrading means spending money.)
Tim Campbell
5D III, 5D IV, 60Da
