There are many reasons blunt weapons are worse than edged weapons in combat.
Take, for example, the fact that blunt weapons require time to swing, and recover from the swing. This makes them inherently slower.
Second, you must also consider that knives are more versatile up-close. You can still cut someone if he's right in front of you. However, you can't get the proper leverage on a bat if the guy is right up in your face.
Third, you can't conceal a blunt-force trauma weapon as easily as you can conceal and carry a knife
Fourth, you can't stab with a blunt weapon, but you can stab with a knife. Yes, you can jab with a blunt weapon, but it's more easily blocked
Fifth, a blunt weapon is more easily taken from you. If you miss a swing, the guy can jump on and grab the weapon from you. You can't grab a knife from someone - your tendons will be cut and you will automatically let go