70% of the market cuz it great,
PC = Origin , UPLAY , Steam, GOG.com,Battle.net, and many Resellers, aka G2A, GMG.
gog.com is great, relying on something being online, to play single player game you bought is not.
Note that "significant market power" bit in your quotes.
With your personal narrow definition of a monopoly (not the one you've quoted), Intel wasn't a monopoly, cause, you know, AMD. Not to mention Via et al.
Yet Intel was CONVICTED for ABUSING it's monopolistic position by EU.
Now, in practice, I couldn't get updates for Xenonauts for a long while, cause, you know, I happened to buy it from gog.com (no DRM ) and not Steam.
Valve is in a position to dictate... and so it does.
It has only digital sales, yet it gets same 30% cut of the revenue as Sony/MS get on consoles.
On Consoles, you have no choice.
No, not really.
On consoles no company has 70%+ of the market.
On consoles I can re-sell, or share games, or buy used ones.
Even if Sony/Microsoft/(gog.com, for that matter) disappear, I'll still be able to play my games.
On consoles, with a very few platform exclusive exceptions, I have a choice from which company to buy.
The question to me is why hasnt Valve pushed the Source engine harder...
Oh, they are trying to.
Not so long ago they've said it would be free "for everyone, who sells on their platform".
Effectively, this will be funded for the 30% revenue off most pc game sales they are getting.
Assuming it would be at least ok, try to compete with "FREE" stuff if you are selling game engines, like, say, unreal.