I'm not a martial artist, nor a boxer, nor a wrestler. In two different police academies I've taken very short courses in disarming others. Twice in my career I've taken a gun away and once taken a knife away from a subject. I've never been taught to tackle an adversary. I suppose there are places/courses that do teach to tackle someone down and then go for the weapon. But in my limited experience and training it's been to focus on gaining control of the weapon in their hand, get it pointed in a safe direction, twist it out of their grip or apply a sharp blow to the forearm to cause them to release it and THEN immediately gain space between me and the adversary.
Again, there may be other ways to teach disarming. I personally don't see myself at any advantage having thrown my body weight at an adversary and ending up on the ground. I feel I'd be at more of a disadvantage on the ground with a bad guy than if I were standing and thereby more mobile.