Potions used to always hit the target they were thrown at, then explode at that location when the timer was up. Unfortunately this means that potions could be timed and "machine gunned" to be thrown and explode as they were reaching their target.
Potions were changed so they target the location, they were thrown at rather than the object. This makes them behave more like grenades rather than heat seekers.
Exploding on impact would be similar but worse than the original issue. You can throw potions into the intended path of your target and time it so that they explode when the target is about to reach them, which is a complete player skill mechanic.