I hear what you're saying, but keep in mind that Bethesda shipped Skyrim as 32-bit in 2011. It wasn't until the Special Edition release in 2016 that it was updated to 64. Now, obviously, we could chalk that up to it just being Bethesda.

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.