According to Apple's stats, 93% of all devices are using iOS 12+. By July 2021 iOS 14 will have been out for some time, so that number will have increased even more. I'd also add that the C3 runtime could have supported iOS 11 if there weren't such terrible iOS bugs in that version, so our inability to support that version of iOS is actually Apple's fault. Anyway with such broad support already and the fact it's only increasing, it's hard for us as a small team to justify keeping around tens of thousands of lines of ancient code just for a small and shrinking percentage of devices. I don't see why publishing a game to "only" 95%+ of devices is a problem; you'll never reach exactly 100% so you have to draw the line somewhere, and this seems reasonable.
For Android, StatCounter have more up-to-date stats and they show Androd 5-6 support is at 17% and falling. As far as we are aware C3 games still run fine on the vast majority of these devices. They only need to have had a software update any time in the past ~3 years. There are various issues with Android having out-of-date software, buggy drivers, or other misconfiguration problems - this has always been the case, and in some cases they also stop C2 games running too. It's mainly because Android is kind of a mess, especially in the old versions. Again it's the same kind of story: these numbers are falling and will inevitably become irrelevant. Even if you published only for Android 7+ (which shouldn't be necessary), you'd still be covering over 80% of devices. There will always have been and always will be bugs and issues to deal with - once again we can't justify keeping around a huge amount of old code just because a small and shrinking number of old Android devices are misconfigured. Even if you set a fairly high minimum version, you can still cover the vast majority of all devices.