Make is a much the lingua franca of build systems as C is for programming, so there's no reason not to provide a (simple) makefile. The alternative they suggest is worse anyway.
How strange. I have tinkered with a couple of FOSS games of Windows and none of them required VS (not to mention another couple of other non-game projects). Maybe that's because they often are multi-platform projects so Make is the best choice at the global level for them?
> The lowest common denominator for build instructions that works everywhere is literally "set your include paths like so and compile these sources".
Yes, but that's quite inconvenient and error-prone ; a typo in a -D flag is very likely to not compile what you wanted.
Make is not a multi-megabyte program with a frack tonne of dependencies. Having your users to install it in order to build your project is far from being completely outrageous (unless for coughmicrosoftcough cults that consider the command-line is evil).
Funny thing is that AtmelStudio (for embedded development of Atmel/Microchip chips) is basically a VisualStudio shell with a makefile generator (built in c#). This is then pushed through make and invokes gcc...
The lowest common denominator for build instructions that works everywhere is literally "set your include paths like so and compile these sources".