The other day something prompted me to review the infield fly rule, which says (emphasis mine):
An infield fly is any fair fly ball (not including a line drive or a bunt) which can be caught by an infielder with ordinary effort when first and second or first, second and third base are occupied, before two men are out. The rule is in place to protect against a team allowing a shallow fly ball to drop in with the intention of causing a force play at second and third or second, third and home. Otherwise, the team would be able to force out baserunners who had stayed put on a routine fly ball.
In these situations, the umpire will declare "infield fly" for the benefit of the baserunners as soon as it is apparent that the fly ball qualifies as an infield fly. The batter is out even if the ball is not caught, and the baserunners can advance at their own risk. If the ball is caught, the baserunners can attempt to advance as they would on a typical ball caught in the air.
The question I have is why is the rule applicable when first and second are occupied and not just any first?
This seems to me like this is ripe for a defense to abuse in order to almost assuredly get 2 outs by letting the ball drop while the runner on 1st waits, thereby creating an easy double play at first and second.
Is this assumption wrong perhaps due to the time for the fly ball to fall, the batter will have ample time to run it out and reach first, thus, the defense is simply in a state of being able to pick which runner then want to have on first?
Is this because presumably due to the fly ball's time to fall, the batter will have more than enough time to run it out and reach 1st? This question discusses the very subjective nature of the rule, but it seems odd to me to not extend that subjectivity to when a situation occurs that could potentially become a free double play, even moreso when the rule's stated goal is to protect baserunners who stay put on a routine fly ball.