Because the last time I wrote a bitmap like that was about a decade ago using a proprietary compiler for a Z80 clone that implemented a "C89-like"[1] language? Call it a bad habit from too many years working with embedded micros.

If I was using a modern(-ish) C, an enum might be more appropriate.

[1] When you only have 16k of RAM and a 256 byte stack, having "int x;" default to "static" storage instead of the stack is a feature.

Assuming C code (not C++), then const int is not the same as a #define. An enum is only good if the values fit within the range of a native int.

static const's may not be optimized to literals. constexpr is not fully supported.