Object Approaching Event Horizon: Why Does it Slow Down?

[Ascenxion]

According to an outside observer, an object slows down as it approaches the event horizon but never reaches it. Why does it slow down?

Thanks.

 

[robphy]

It appears to slow down because (due to the arrangement of light cones near the horizon) it takes successively longer for the information from the infalling object to reach the outside observer.