What exactly is bad about the fact that Steam takes a cut of the money?
Someone decides they're going to put money in their steam wallet, either through steam card or bank account.
They put that money in knowing full well that they can't get it out again and are going to use it on Steam products. Steam will eventually get this money finally given to them, and it's trapped within the steam system until that point.
Now say I have £10 on my account. I could be expected to spend that full amount on a game, putting a tenner finally into Steams coffers.
But, consider now that I want to buy a few items on the market. Some emotes, TF2/Dota items, card packs, etc...
I spend £10 expecting that the people who I've bought from will have that money to either trade again on the market or buy a game. But they don't. That £10 is now less, because Steam has taken a percentage of each transaction. The money was stuck in their system and could only ever find it's way into their pocket, but Steam have taken a cut early, just to satsify themselves. Now those people I bought from have less than the £10 I gave them. A portion of the money I have put in to the system has been taken out without any users receiving anything for it.
But you made the point that Steam gave me the item anyway as a reward.
But hang on, for almost all market items (bar the free games like TF2, although keys and items from key chests still cost actual money), I had to pay money for them.
I could've spent £60 or more for the individual games that those cards came from. And on top of that I have to play the games in order to receive the cards. Those cards come with the game, so I have paid for them.
So consider that I've paid for these cards, and I've played the games to earn them. I've waited for a booster pack to be sent to me (which again only happens if I've bought the game, so they're not free), or I've purchased cards or booster packs from the market with real money (which either I or another user has introduced into the Steam system), in order to craft a badge and recieve an emoticon or wallpaper.
So, I could have spent the likes of £65 on getting these items, plus spent hours playing the game on steam to earn the cards and boosters.
I decide I want to trade the item on steam through their market, which is my right to do on their system.
I see that people are selling the item at £1, so I do too. I expect to get at least a quid from someone who wants it, when this item has cost me so much to get anyway. Surely that's the least I could recieve for that effort and expense.
But no. That person sends me £1, and I recieve 90p or less.
I've spent a lot of money to eventually get this gimmick, and all this money is locked in to Steams system, and the forgeters are still going to take 10% or more from my meagre transaction, just in case I earn too much money for me to eventually spend in their shop!
