I'm gonna play devils advocate a bit with this. I'm a long-term Mac user...but I'm also a long-term Windows user as well, having served as an IT administrator for the better part of 5 years some years ago. I've been in both worlds and can certainly understand the frustrations developers have trying to develop a single app that works well in both environments. However, there are reasons for everything that both Microsoft and Apple does. Understanding those reasons is key to dealing with the problems with any of these environments and how to solve them.
The (significant) work required to do an Isaac/Mac code-rewrite delivers exactly zero incremental customer benefit. Re-writing code to 64 bit is a resource-intensive, make-work exercise forced on Apple developers, in the service of Apple's grand technology diktats.
Actually, there are benefits to going all 64-bit and leaving 32-bit apps behind.
For starters, all 32-bit apps are limited to 4GB of RAM. Now, that might not seem like a problem with an app like Issac. I'm not sure if any user utilizes that much RAM with Issac.
The other benefit is the full utilization of 64 bits per cycle. Currently, in both Windows and Mac, running a 32-bit app requires translating each instruction into something a 64-bit processor can utilize. That requires extra stuff being added to the OS and does add a little overhead to resources when the app runs. When you consider the fact that virtually every computer being sold has a 64-bit processor in it, it doesn't make any sense to continue supporting 32-bit. Dropping support for it allows both Apple and Microsoft to further optimize their OS's for better performance. Apple is doing this now and I don't doubt Microsoft isn't far behind.
I would also add that Apple's security changes introduced in High Sierra produced an unexpected demand on us, to which we have responded as best as we could. We've seen some major software companies also deal with the same security issues, and their workarounds aren't pretty.
Yes, Apple has made some security changes...and for good reason. Without them, users stand a greater risk of being vulnerable to bigger security issues. The whole Adobe Flash debacle taught them that. You just can't trust third-party developers to do what is necessary to secure their apps. Even big companies like Adobe can't be trusted. As such, Apple decided to lock things down so that users are in more control over the security of the apps that run on their machines. Part of that is due to their attitude about the users of their computers. Not everyone is tech savvy and Apple knows it. They aim to make their computers as easy as possible to use for those who don't know how to use computers.
What is easy for Apple to mandate places huge burdens on others. They don't care.
I tend to disagree. I think Apple does care. Probably more than even Microsoft or Google. They're super vigilant about security and privacy. Now, that's not to say they're perfect about it. They're not. The latest debacle with the release of Catalina and the latest iOS releases prove that.
The thing is that they've been giving people notice about dropping 32-bit software for quite some time now. They told people they were eventually going to do that as far back as High Sierra with notices being turned on for 32-bit apps running on Mojave. Basically, developers had two years to transition to a 64-bit only environment.
The question I have is this:
What percentage of your user base is on the Mac? My guess is that it's a fairly low number. But even 10% of your user base is quite a bit. Ignoring it could mean an instant 10% reduction in future sales. That's not exactly good. I make the case with my web design business that ignoring people with disabilities is an instant 10% reduction in visitors. Why ignore a whole group of people?
Consider your statement that the upgrades provide
zero incremental customer benefit. The problem now is that the current software provides
zero customer benefit. If they can't run it, they can't use it. That's not a good place to me in my opinion. Hopefully that'll change soon.
In the meantime, people like me who are pretty tech savvy can run Issac on a virtual machine. I fortunately use Parallels Desktop and have both a Windows 10 machine and older version of MacOS running. But not everyone is in that position or even knows how to deal with it. Till you come out with a Catalina compatible version, you're effectively leaving customers in the lurch.