complicating/complicated factor

Perhaps the most important complicating factor is that backbone routers must operate at hight speeds, being capable of performing milions lookups per second.
I wonder why did the write use “complicating” not “complicated” in the sentence?
Is there any difference in meaning between them?

“complicating” means that this factor makes something else (such as the situation in general, or the general operation or setup of the network) complicated or difficult to achieve.

“complicated” would mean that this factor itself is complicated.

Thanks, Dozy, for clearing up my doubt!