That's a bit of a simplistic view.
More cards doesn't necessarily lead to more profits for valve. The value of the cards is directly linked to their scarcity in the "card economy". Flood the market with more cards and the price drops, along with valves cut.
Valve also has a strong incentive to maintain a perception of fairness. They aren't in the card business they're in the game selling biz. And for that a market that is seen as fair is more valuable than extracting a couple cent of a card sale.
I don't think they'll do anything about it anytime soon but if it becomes wide spread enough I think they will
There are hundreds of thousands of bots on Steam. Not just bots that play the market, but the whose soul existence is to idle for cards on games that are given away for free. If Valve cared, they would've done something about it. They turn a blind eye, because it makes them money. I think your logic that Valve wants to keep prices at a higher sweatspot is flawed. When cards are cheaper, more people buy them. For instance, in which example do you think Valve gets a larger cut: 500 cards sold at 10c a piece (where Valve gets 3c a card), or 5000 cards sold at 4c a piece (where Valve gets 1c a card)?
I think your opinion that Valve care's about fairness is quite misguided. Every month they're in the news about a new 'feature' that limits peoples ability to use their service. Ahh look, No more cross region trading. Ahh look, keys from the market and Steam gifts have a two week refractory period. Ahh look, we don't give refunds for games that don't work, who needs customer support? Hey, you like hats and gun skins? We have plenty of those!
The market is fueled by the players. Without them, the market is nothing. Valve don't care about things appearing to be fair, because they already aren't. As long as they keep on printing money, their only interest is their bottom line. If the day comes when they stop making huge amounts of money, then they would start caring.
It's all fun and games until VAC detects a modified dll and shitlists you
You shouldn't be messing with VAC enabled games in the first place. The way the VAC system is designed, they can't tell the difference between a modified dll that adds bloom, or a dll that turns you into an aimbot god. Luckily though, very few games use VAC. Plus VAC bans are on a per game basis anyway, so at least you don't get completely screwed. Also the dll's that are used for VAC, and the steam_api dll, which every game on Steam uses and how Idle Master and SAM work, are completely different.