Comment by ajross

They didn't develop it from scratch though! The 2010 Mac HL2 binaries are a port of the existing 32 bit Windows product, with all the word size and alignment issues you'd expect for C++ code of that vintage. You don't magically wave a wand and expect high performance code to work when sizeof(void*) changes, and the effort to do that needs to be weighed against the perceived value and the size of the market.

Needless to say, annoying a bunch of HN nerds a quarter century in the future wasn't on Valve's radar. They just wanted some Mac revenue and picked the low hanging fruit.