It could have something to do with how the sort function for size is set up. Like if it's getting that info from the folder size on your computer. Which wouldn't work for games not installed.

Or Valve didn't think about that or didn't want to for some reason.

Support won't really have any info for you either as this very much falls outside of what they handle. (Account and billing issues)

Unless Valve ever makes a public statement about it your guess will be as good as mine or anyone else's.

Because they never had the filter for it.

It was only a few years ago that they added installation size as well.

Because installled estimatate is not same as local installed file, i bet they count mods and other i bet its same as folder stats fo content size maybe in the OS. and tht cant be compare with game requirements installment infomation.

Dont forget you talk with tech dudes here they will not see your topic as you do, i can also do estimated size that actual dont hold water, in the many i use apox around 10TB to all my games, as you see why reality dont match a estimated guess.

I already had 6TB games in 2000, im sure you can do the math here 10TB is not enough for all games, so you see we humans is very bad at best guessing total size for not installed game and then you add up all games it goes really bad in guessing , and NO i do not want to caculating games not intslled yet.

And thats why not installed game size is irrelvant.

And be happy i and other bother reply to you. ( i bet you dont likw the reply same as i dont care how many storage room you have in your house hold for cloth. ) you have not buyed yet.

So technical we have no clue or want to know if you have room for it. ( this is user own problem ) to have enough storage room even at steam.

And stop think we are rude here, most ppl get what i and other see this.

What prevent you from buy more disk drives as you see fit, assume yuo bought a desktop PC that can handle it. ( this is why this is not a steam issue at all and never has been, store game requiments is a estimated size, nothing else and it dont matter if game devs have wrong information about it. )

So you see ppl with IT knowledge already know all this. ( they dont care about xmas or other updates that expand size or high texture pack added to game. )

I know you ment well with topic post, things has change over the many years, and game devs has every right to do what they want with there games. ( you have a license to play them thats all. ) its not even your files.

Try understand this will help next steam user that think they can controll size you can't. mistake in what store page say is a estimated guess. best advice we can give you. and the other side of this nothing you can do about it. unless you will not install it.
and we are back at not intsalled games dont matter.

You can find millions of steam user that cant install all there games, disk drives is near full and they might not want to add more drives, or dont have funds or they safe up to new PC.