Buddha is Love, Buddha is Life.

"If we are denying keys for normal size batches it's likely because your Steam sales don't reflect a need for as many keys as you're distributing, and you're probably asking for more keys because you're offering cheaper options off Steam and yet we are bearing the costs. So at some point we start deciding that the value you're bringing to Steam isn't worth the cost to us.

For example, say you've sold a few thousand copies on Steam but have requested / activated 500K keys, then we are going to take a deeper look at your games, your sales, your costs, etc." - Valve Dev

Source: https://www.vg247.com/2017/08/18/in-order-to-reduce-game-sales-outside-of-steam-valve-will-no-longer-automatically-fulfil-key-requests-from-devs/