A bigger source of their profit is taking 30% of most PC gaming revenue with minimal overhead. This was such a money spinner that other game publishers eventually got wise to it and started their own stores. But Steam is still the big dog here.
Not to suggest that a good slice of Valve's profits don't come from Steam, but they still make a reasonable amount from individual games.
[0] That's a 2015 figure, with suggestions it has increased since then: https://venturebeat.com/2015/03/24/dota-2-makes-18m-per-mont...
[1] In 2017 it was possibly more than double that figure: https://www.superdataresearch.com/market-data/market-brief-y...
Every TI, the prize pool surpasses 25m. Which means that just by buying compendiums and treasures, people have already paid 100m (25% is contributed towards the prize pool).
There's also multiple compendiums per year, or battle passes or whatever depending on the year.
And there's a lot of random loot box releases, Arcana items etc.
On top of that, Valve extracts an extra 10% (or is it 15%) of the trade value of every item that gets sold through the steam market. And those items are sold and bought A LOT.
