Why is weightlifting not good for healing a wound?

Weightlifting wounds: It depends on where the wound is located and the type of weight lifting that you are interested in doing. You would need to be more specific to get a better answer.

Stress and strain: Overall, the keys to fast wound healing are to keep the wound covered and moist, keep the adjacent skin dry and protect the wound from trauma and stress. Weight lifting potentially involves ]lots of straining and movement with heavyweights. Once the weights are moving, they are hard to stop and so you risk torquing and twisting your body as well as direct trauma from the equipment. Be careful.

Has no bearing.: There's just no link between weightlifting and healing of a wound. No relevance.

Wound healing: can be aided by reduction of swelling, resting the region to a point and avoiding factors that may torque or shear the wound. Depending upon the wound, where it is, what the cause is and many medical factors, there are times when weightlifing is curtailed until the wound is on its way to being better. This is a very specific issue that depends upon what the conditions are. Best to ask each time.