Earlier quoted context omitted.
This idea that "6+" years old is particularly old really irks me, because it's not. Most other things in my life that I rely on last longer than that. I also occasionally need to run software that's older than that. 6 years isn't nearly long enough to even consider dropping support on the OS level. Try twice that.
Apple is not looking at 6 year old applications and saying “It’s been long enough, time to drop support for this app”. They are looking at the 30+ year old architecture that is 32-bit x86.
No mainstream operating system that ran on 68000 processors in the 80's, PowerPC in the 90's and Intel since 2006 is even around today.
Y’all must have forgot how NeXTStep, which later became Mac OS X and now macOS ran on 68000, Sparc and MIPS back in the day.
The same way Apple was running Mac OS X on Intel hardware long before the first Intel Macs were released, there's got to be Arm-based MacBooks or Mac minis running macOS right now.
So it makes sense for Apple to get rid of as much technical debt as they can before making that jump.
And because of Catalyst, which enables iPad apps to be ported to macOS, there will be more apps for the Mac.
Some of the Catalyst apps have some rough edges and not all of the frameworks are available yet, but things look promising: https://9to5mac.com/2019/10/07/macos-catalina-catalyst-apps/.
Finally, Apple has been telling developers since Snow Leopard was released in 2009 about transitioning to 64-bit.