While it’s hard to imagine, free throws weren’t introduced to basketball until 1894, three years after the game was invented, and then they were a 21-foot shot! That’s slightly farther out than today’s college three-point shooting arc, which is 20 feet, 9 inches from the basket. The 21-foot distance was only used for one year, though, and in 1895 the present distance of 15 feet was adopted.
What primarily makes this distance so ideal is that it is short enough to lead to a relatively high shooting percentage in games from the high school level to the pros. That’s how it should be for a shot meant to discourage players from fouling. The distance also is short enough to allow players to shoot comfortably while keeping their feet on the floor, thus making it more possible to develop repetitive mechanics through regular practice. Even seven-footers, who sometimes struggle to make free throws (Wilt, Shaq, Dwight Howard et al.), can become quite proficient.
Another plus to the 15-foot distance is that it makes the free-throw lane just the right size to fit three players on either side and creates a lot of close-quarters rebounding action.