Why are some games (such as any simulators or indie games) on Steam and other games (rather large, such as Sims4 or Minecraft) not?
It decides the manufacturer or publisher of the game where they offer their game or the seller what they want to offer.
If the contract of Steam is not attractive to the people, it will not be used. Or they pursue their own agenda and want to sell their own shop with exclusive titles.
Steam belongs to Valve. Steam has a long range, which makes it interesting for small developers. Some (big) game-makers want to distribute their games on their own platforms, so the games will not be on Steam then, e.g. Here you can call for example EA or call Ubisoft.
Of course, the whole thing has to do with licensing and costs. Not every game developer is willing to pay these fees.
For many games, it is also good if they are not sold on multiple platforms, as between the platforms cross-play is not always possible, without this again costs incurred by licenses and program adjustments.
PS: The developers do not always distribute their games through publishers, but distribute them themselves, which is why the publishers once ignored to clarify the scheme. Steam is a publisher that not only distributes its own games, not all Sun's. There are developers who are also publishers or developers who are contractually exclusive to specific publishers, etc.
So it gets more complicated the deeper you dig in:-).
Hello mk100a, Sims is not on Steam, because EA itself has a download shop, called Origin, here you can buy Sims then, Minecraft is available in the Windows Store on Windows 10, or on the Mojang Homepage.
