They had to take the cumulative risk of getting caught though - one well-targeted burglary to take a designer handbag or diamond necklace would earn that thief as much as the indiscriminate 'stealing nwallin's gym clothes' thief would make in a year, as long as they had the network to sell the contraband on without incriminating themselves.
That risk is there regardless of what they steal. The kind of thieves who break into cars are low-effort-random-reward. They have neither the patience nor the skill nor the resources for the kind of planning you're referring to. Yes, the bag didn't contain much valuable. A different bag might have. Had the thief known that for a fact beforehand they probably wouldn't have bothered.
