In principle I agree that it's preferable to have the old game as a visible download on the store but you should understand that it's unusual for evolving online games to offer older versions in any manner these days, nevermind let players host games independently. That Valve provides this possibility at all, even if in a convoluted way, already puts them miles above Blizzard.
CS 2 even allows for players to carry over their whole collection of skins, which is something many players care deeply about and even invested significant money on. Which is itself a questionable matter but I can't deny that this is important for the players. Maybe this is why it was made into a new version of CS:GO rather than a separate thing.
I think it's fair to demand that old CS:GO is added to Steam in a more transparent form, but it's a matter of convenience rather than them taking anything away from the players like Blizzard did.