Steam has always been a pig with data.

When I used to live with my parents I specifically bought the physical Orange box so I could play portal and half life without having to download anything over the horribly slow and metered satellite connection.

Steam immediately forced a multi-day process of downloading and updating steam, then downloading and updating portal, before I was able to launch the game and have it crash from broken GMA950 drivers.

I buy maybe one game a year these days but I always buy it from GOG pretty much because of that experience.