> A strange tip had arrived from Belgium’s gambling commission.
I can't speak to Belgium specifically, but in many areas one of the responsibilities of the gambling/gaming commission is ensuring "fair" gambling. So they probably care more about the impact of match fixing on the "fairness" of sports betting rather than the reputational (I assume that's what you meant rather than "repetitional") risk to any particular sport.
When betting is involved, I don't see match fixing as all that different from someone bribing a casino employee to use dice loaded in their favor or help them cheat in a game of cards. Or depending on who's involved, maybe it's more like the casino using dice loaded in the casino's favor.
In any case I think it basically amounts to fraud. The published odds are inaccurate because the outcome has been fixed, allowing the people aware of that to make money at the expense of the people unaware. Fraud is generally a crime, so as long as the match fixing isn't reflected in the published odds IMO it isn't all that surprising that it's a crime.