Well i do not see a multiple choice setup here so i'm going to assume it is a free response. But generally from my experience with not only my step father working at a data center but me doing research on this topic at hand; i've come across a lot.
The main reason network security is a huge issue regarding data centers is due to the fact data centers are used to store very valuable information such as credit card, and billing statements from online based companies. If there was to be a breach like the one with Sony several years back, than millions of peoples credit cards and billing statements would be leaked. The second reason being that if the data base is breached copied than corrupted said data center or corporation could lose millions, if not billions of dollars due to the loss in data.
I hope this helps, if not go ahead and message me if you need more info.
