Yes, Valve is quite consistent about keeping things locked to its store. Steamworks is also limited to Steam. Proton is an exception, but the LGPL license of Wine simply wouldn’t allow it to be otherwise. Publishing the source code is required if building on it rather than just using it as a component.
^ Mental gymnastics
The inverse is also true. Go buy Half Life on Origin. Can’t? Oh no! Monopoly! blows siren
Yes, Valve is quite consistent about keeping things locked to its store. Steamworks is also limited to Steam. Proton is an exception, but the LGPL license of Wine simply wouldn’t allow it to be otherwise. Publishing the source code is required if building on it rather than just using it as a component.