Think BASIC plus supporting machine language code, or code plus assets.
If you take it to the extreme, there was a thing called an IFFL loader (e.g. https://github.com/luigidifraia/iffl-system ) which allows you to put a whole file system with multiple streams into a single C64 file. This had some advantages at friction points like where when the file had to switch location between BBSes and Disk Swappers as you didn't need create disk images first and could simply copy the single part files. Always used to be somewhat exotic though when I still was in the C64 scene - not sure how it's nowadays.
One example of boxed-games shop: https://rgcd.bigcartel.com/category/commodore-64
A page of a C64 games producer on Itch: https://psytronik.itch.io/
Let's suppose then that you are living somewhere where you can live comfortably off a couple of thousand dollars a month. There are many, many parts of the World like this. Many you can live quite well on just a few hundred dollars a month.
Now let's suppose you can build a game in 2 months, and it will sell over its lifetime - say, 5 years - a thousand copies. And each copy nets you $2. It doesn't take a genius to work out that this not a bad lifestyle business investment of time and effort.
I think these guys are going to do OK, depending on where in the World they are. Most people in the US and Europe are spending an order of magnitude just to survive than the rest of the World, and think the hot stuff is in the software that takes years to build with multiple rounds of VC funding - there are alternatives.