I'm in "campus" law enforcement, and bike theft has always been a problem. hundreds (maybe thousands) of bikes in one handy location, frequently poorly secured or not secured at all.

Cables are absolutely useless. I have seen 12-year-old kids cut em with nothing more sophisticated than an old pair of pliers and determination. A 12" bolt cutter snips em' in one easy cut.

I'll often see things like a lock put around one fork leg. Pop quick-release, lift bike, and reassemble....

We get kids who will ride old beaters till they just won't hang together anymore, then they'll dump em' and take a newer bike. They often go for the cheap but flashy-looking Mongoose or Huffy.

Pro bike thieves will go for high-end bikes, and can defeat U-locks by various means. Why anyone would take a 2000.00 MTB to use for campus commuting is beyond me, or why they'd leave it at a bike rack for weeks on end... Got more money than me, I guess.

Last guy we arrested would would walk onto campus with a backpack, looking for all the world like a student. In the pack was a bike helmet and a pair of bolt cutters. He'd snip a cable, put on the helmet, and ride about three miles to the corner where his dealer hung out. Straight exchange; bike for rocks.
We got him with a stakeout.