Fewer than there would be if Steam actually shipped ARM support to those who wanted it.
It's a classic chicken-egg problem.
I have a game on Steam, it builds and runs on ARM/RPi just fine, but there's no ARM in the list of architectures on Steamworks because the client doesn't support it. So I don't bother shipping the ARM build despite having one here and one of my artists using an RPi4 as their primary desktop with a functioning build of the game for testing.
We're talking about commercial interests here. If a game has been ported to native linux/SteamOS, it's likely just a recompile away from having ARM support. If the Steam client were made available to Pi users the demand would appear on the store for more ARM-compatible games and we'd all immediately jump on the opportunity for more sales from practically zero effort.
It's a classic chicken-egg problem.
I have a game on Steam, it builds and runs on ARM/RPi just fine, but there's no ARM in the list of architectures on Steamworks because the client doesn't support it. So I don't bother shipping the ARM build despite having one here and one of my artists using an RPi4 as their primary desktop with a functioning build of the game for testing.
We're talking about commercial interests here. If a game has been ported to native linux/SteamOS, it's likely just a recompile away from having ARM support. If the Steam client were made available to Pi users the demand would appear on the store for more ARM-compatible games and we'd all immediately jump on the opportunity for more sales from practically zero effort.