I love steel but to be fair, he won't ever be unbanned for valve majors and from a business perspective, he probably shouldn't....
Think of it this way, Valve makes cs:go which makes a ton of money in the skin market. Then gambling comes in and elevates the publicity around the game because even non-gamers and non-players can "actively" participate in the game via gambling. This is great for valve because it gives more visibility which increases the playerbase (more people buying skins). Even though valve doesn't make money off the gambling, the gambling market is very much responsible for a lot of cs:go's success.
1 Match fix proven to be true jeopardizes the entire gambling market. If gamblers cannot trust that the outcome of a given match is going to be skill + random circumstances, the gambling market will fail. This will drive down the viewership of tournaments which will reduce tournament organizer revenue's which eventually effects Valve's wallet via the skin market. Evenetually, the game dies.
They literally have to take the 0 tolerance stances if they want to dissuade people from doing this. We all know how intelligent, compassionate and honest the CS:go community is.