Sure, it's a fair question. It's also one I could spend more time that I want to on, should I list something that someone disagrees with or doesn't think it's good enough reason. But let me give an example of something totally different. I can't use the latest version of Blender, because they decided to not support my video card (early 2009 Mac Pro).
But what I was mainly getting at is in supporting old OS versions. That doesn't necessarily mean a given feature can't be used, it might just mean that it causes more baggage or inefficiency, and it might just mean that the programmer has to do more work. My latest plugins support back to Mac OS X 10.8, for instance, and some have argued it should be at least 10.6 (ten years old). I see Ozone 9 has a minimum of 10.11, as does Pro Tools. Reaper supports back to 10.5.
BTW, one important thing many people don't consider in arguing the validity of supporting 32-bit still longer: Yes, a good number of people are still on 32-bit plugins. But I'd suppose that a large percentage of them—compared to 64-bit folks—do not actively buy plugins. So, if one were to say that the 64-/32-bit shares were 80%/20% (to use an arbitrary ratio), you still can't say ignoring 32-bit is ignoring 20% of the market, because the question should really about buyers. And it's likely that buyers tip the scale much more heavily towards 64-bit.
Fortunately, I only need Cocoa to test the pointer and to set all up and I don't have to link against the Carbon framework. If I did, I'd drop 32-bit in a second. But, I'm still supporting 10.6 32/64 bit and XP 32/64 bit and I'm going to hold out as long as it's possible. I'm sure Apple is going to start putting their ARMs into laptops at some point, so the new Universal will be Intel/ARM. At that point, I'll freeze the 32-bit version and soldier on. I can certainly understand devs selling plugs dropping support for older OS versions. I'm sure they've looked at the cost of development and support vs revenue losses and gains.
