I've had cheap components stolen before. A friend of mine had is beater stolen recently - it was locked with a u-lock and the bicycle couldnt have been worth more than $50.

And the professional thief will have tools. The MO is basically driving around in a van with a carjack, 4' bolt cutters, or battery operated power tools and targeting bicycles locked up. 5-10 minutes of work and they throw the bicycle into the van.