This is true, but for idtech 3 and 4 games there were official Linux binaries, but they arent distributed by platforms like steam, even though they already ship Linux versions of other games. Quake 4 or Doom 3 was I think the last of the official Linux binaries from Id.

There are better source ports if you just want to play vanilla doom games.

I know, you can set the native version up outside of Steam, (and they'll probably be superior if it's a source port). It would still be nice if the version Steam gave you was a native Linux version.