Only anecdotal, but there may be cultural problems stemming from the flat structure at Valve that make organizing around products difficult. This video came out 4 years ago so I don't know if anything's changed since then, but it's one ex-employee's experience of their work culture at the time.
Basically he claims that even though there's a flat corporate structure within Valve, in practice an implicit management structure arose in which those with the most political clout controlled others without it. Plus they used stack ranking at the time.