I'm not sure how it works in other countries, but in Australia you generally don't buy a phone. You buy a plan from a telco, and the plan comes with a free phone. So a stolen phone means the owner will sign up for a new plan and get a new phone, which you, the telco, have to pay for. So as a telco, if you can keep someone on the same plan with the same phone for as long as possible, you save money.
Hence reducing theft means Aussie telcos can spend less on buying phones from Apple or whoever.