Why aren't Steam achievements recorded?

Halo Waypoint accounts show users their overall Halo Gamerscore, although the three Halo titles (Spartan Strike, Spartan Assault and Halo Wars: Definitive Edition) that are on Steam are not recorded - there isn’t even an option to link Steam accounts to Waypoint.

The description “total Gamerscore earned from all Halo achievements” is a fallacy since it doesn’t track Halo achievements awarded on PC’s most popular gaming client.

I understand Steam doesn’t have a “Gamerscore” system such as Microsoft/Xbox has, although it would be easy for the achievements in these Halo games on Steam be given the corresponding Gamerscore value as their Xbox counterpart.

In the future, I would like to see Halo Waypoint track Halo achievements across all clients.