With the advent of VOIP, cable modems, and likely a few other systems I'm not aware of, "cutting the phone line" has become more complicated. The phone line could very well be the cable TV line, for example.
I had a client site that was burglarized twice. First time the cut the phone line to ADT, then smashed the main entrance door with a clay flower pot by the door and they got away with two cash drawers. I installed the cable system with 4 IR cameras,connecting them to ADT, using a UPS to power the alarm. and to the owners home, 6 mths later they got hit again by cutting the cable and phone lines on the roof.
The biggest issue with business owners is when their alarm activates and police respond then they get charged 500.00 per call if it's a false alarm. BG's know this and also have a lot of experience, usually from being educated in prisons. Smash & Grabs get caught.
Keep in mind dogs are not exactly that hard to kill.
You're right they aren't. However. I worked for the City at one of the remote sites, and we had a very complex alarm system. We were hit a number of times by burglars after the aluminum light poles. They would cut a hole in the fence then with portable saws cut up the poles than haul them away in a truck.
The business next door to us was an auto recycler and scrap metal buyer, He had a lot of exotic metals and never once was broken into,and had been there for over 40 years. His only alarm system were 4 "junk yard" dogs, and mean as hell They were fine during normal working hours and didn't bother a soul. After working hours you had better not try to break in. He said he only one attempted break in years ago and two people were mauled so much they ended up going to hospital. Word got around.
I recommended to the department head to do the same thing and they would save thousands in security contracts. They said no because of possible liability law suits. Well, they still get broken into.