Why does Half-Life provide files for mods?

[Bhoppi]

In the Half-Life installation dir, there are directories, such as bshift, cstrike, dmc, dod, gearbox, etc, with files in each of them, even if I don't install these mods.

Though it doesn't provide files for all mods like Condition Zero.

So I'm curious about it.

[instabilis]

I guess they could be to do with the HD model pack.

[Pocket]

Leftovers from the pre-Steampipe days? If I'm not mistaken, those games were treated as mods and housed in those subfolders originally.