You're right. As david_shi also points out, there's so many other less bothersome ways it makes little sense to recourse to violence on online bets.
Looking into it, the vast majority of incidents are the player themselves betting against their team or losing on purpose, the same of ways matches have been fixed since the dawn of betting. Paying someone is just so much easier than fighting them.
While the opportunity for this isn't zero, the reality is that there are safer and more lucrative ways for criminals to make money, especially for those who have the aptitude to pull something like this off.
If hurting someone credibly increases the odds, it's not if but when will people cross the line.