The limit isn't really a resource issue, since you can run pretty much an "unlimited" number of non-Mac VMs. I suspect it's more of a business decision, such as preventing people from setting up shop as a low-cost Mac VPS provider.
I can run a ton of Windows VMs at the same time, wouldn't Windows be a comparable resource hog to MacOS?
Apple M2 CPUs can have up to 192GB of RAM. If we look at the Mac Neo that has only 8GB of RAM, then an M2 host should be able to run at least 20 VMs before memory gets scarce.
There's no good reason Apple limits to 2 VMs except for greed, which they are well known for.