Because the Steam sells PC versions of games.
Even if there is a game on Steam that has a mobile version, the version on Steam is ported (sometimes poorly) for PC use.
If you want mobile versions, go use the existing mobile stores to obtain the mobile versions.

Well, I mean... Google Play and Apple Store do it already. And if Steam ever gets on phone the way you suggest. Chances are you are going to have to download it through those stores anyway. Might as well stop piling up the middlemen and just use the store.

引用自 Thermal Lance：

Well, I mean... Google Play and Apple Store do it already. And if Steam ever gets on phone the way you suggest. Chances are you are going to have to download it through those stores anyway. Might as well stop piling up the middlemen and just use the store.

Not necessarily, EGS managed to get itself on Android, without the Play store. Not that hard to get it installed.

Also if they even try that with IOS (make a store) Apple will sue them as it is a closed ecosystem and Apple want to keep it that way. Not saying it's impossible, however it would be very hard and doubtful Valve is even interested in taking the risk.

引用自 JPMcMillen：

引用自 Thermal Lance：

Well, I mean... Google Play and Apple Store do it already. And if Steam ever gets on phone the way you suggest. Chances are you are going to have to download it through those stores anyway. Might as well stop piling up the middlemen and just use the store.

Not necessarily, EGS managed to get itself on Android, without the Play store. Not that hard to get it installed.

That's because Epic is greedy for money due to how bad the EGS is failing.
They don't want to pay the 30% fee.

And the only mobile game the EGS has on mobile is Fortnite.

To be fair, with how Steam Frame is Snapdragon powered device and they actively developed/supported software to allow running PC games on it, it could be possible to have steam games running on Smartphones, so a Steam client on Mobile that would facilitate that could be interesting to see.

Great idea so that the steam store gets completely polluted by poor quality mobile games that are all gachas, p2w and add infested. We already have bad PC ports so please don't ask for this. If steam is generally speaking one of the most beloved game launcher it's because it made some good decisions at some points that favor gamers and not companies. If you prefer gaming on a mobile phone then you kinda deserve to suffer Android and Apple total no consideration towards consumers. End of story.

引用自 JPMcMillen：

Not necessarily, EGS managed to get itself on Android, without the Play store. Not that hard to get it installed.

Lots of third party appstores on android. On iOS is a very different tune, though.