...........Also, just to reiterate, my point isn't so much about the procedures as the "why". Why you can take a drop near the point of entry in the case of a hazard and why you can't take a drop near the point where you "think" you lost the ball or where it left the course.........
It doesn't answer your question "Why?" but the difference has the authority of antiquity. When a group of golfers known as the Gentleman Golfers of Leith put together the first known set of Rules in 1744 they recorded that same difference between losing a ball and putting one in the water.
If your Ball comes among watter, or any wattery filth, you are at liberty to take out your Ball & bringing it behind the hazard and Teeing it, you may play it with any Club and allow your Adversary a Stroke for so getting out your Ball.
If you shou'd lose your Ball, by it's being taken up, or any other way, you are to go back to the Spot, where you struck last, & drop another Ball, And allow your adversary a Stroke for the misfortune.