[Aardwolf]

I have no idea if this was the reason behind turning the dark yellow into brown, but the brown was a much better looking color for DOS games so it was a good call

They could also have done something about the two magentas though... E.g. made one of them orange?

[tracker1]

The light red usually appeared somewhat orangy/peachy, it's generally used as flesh for ansi artworks.

ex: https://16colo.rs/pack/ice-200207a/ti-war.ice

[tracker1]

I think it was just determined that brown would be more useful than the darker yellow in practice. Other xterm colors are also a bit off from CGA/EGA/VGA DOS colors.