Well. If you put a large glass window on the reinforced steel safe to make sure you can observe inside the safe. You can’t exactly expect criminals to not just smash window instantly to take everything instead of struggling to open the safe harder way.
Making master key is also not the approach that works because unlike physical keys, digital keys can be copied millions of times exactly without any flaw over miliseconds without requiring any specialized tool on site.
I would also wager that Valve was worried about Microsoft attempting to use “creative” methods to compete with Steam and chipping away at them, like hidden API. Its not like Valve knew that Microsoft’s attempt would continue to flop so hard for decades that they couldn’t even try that.