I am not sure where to start, you are questioning the very definition of bowling, which means releasing the ball without bending the arm or elbow joint. Pitching or throwing means releasing the ball with bending the arm or elbow joint. These are high level definition of these two terms, if they were same thing, we did not have to use two different words, duh....
Why cricket uses bowling Vs pitching, there may be historic significance which I don't know myself...In baseball, your pitch never land on the ground, where as in Cricket bowling mostly land on the ground before reaching the batter. With baseball style of releasing the ball (pitching), you may not be able to bounce a whole lot, you have to take the arm over shoulder to hit the ground hard or bowl that heavy ball...Throwing is more useful when your trajectory is aimed at object that is above ground...Even at 100 MPH, MLS pitchers will not be able to bounce much with throwing action...
Also, over the arm bowling was developed later, earlier people use to bowl under arm for most part...Over the arm is more natural evolution of under arm...
Cricket chucking is mix of pitching and bowling, you are trying to do both, get more momentum and bounce behind the release, that's probably the reason its not allowed even from the early days, too much advantage to bowlers...Plus, with chucking you have change the nature of the ball in the very last minute(what Hafeez used to do), which is hard to do with pure bowling, again unfair advantage...Same goes for no LBW if ball is pitched outside leg stump...
If you look at scores in 1800s, game was lot more bowlers friendly, wickets were sticky and very uneven...Laws evolved (both playing conditions and bowling rules) to balance the game in favor of batters... Now we are trying to balance the game in favor of bowlers in era of T20, flat wickets and small grounds...15 degree bend is allowed, bat sizes will be regulated soon, two bouncers allowed, etc... Keep in mind Cricket prospers when contest is even between ball and bat, you have to keep tweaking the rules to maintain the balance
