Because, for an external observer, time infinitely slows down near the event horizon. In other words, during one hour by the clock of the far-away observer, the time that passes by the clock of the falling observer approaches zero as he approaches the event horizon. So, when you look from the outside, objects get 'frozen' as they approach the event horizon. For the falling observer, nothing special happens at the event horizon, and he just falls through.

If you happen to approach the event horizon closely and come back again far away to where you started, you will see that a lot of time passed at your origin, while by your clock, the trip might have been short.