[Ethee]

Based upon everything we know from Valve's corporate structure, they're basically their own self-contained YCombinator. They have a ton of internal 'startup' groups that are constantly trying new and boundary pushing ideas. Looking at it through this lens, it's not really a good company fit for any junior. Having juniors detracts from your seniors work, but the point is that you're supposed to get value from that when they eventually become mid-level or senior engineers themselves. But if you're constantly working in new complex environments it's hard to bring a junior up to speed and teach them the requisite skills to thrive, especially if that project they just spent 3 months getting up to speed on gets canned because the idea didn't actually pan out.