Lowest cost/highest profit is what drives corporations. It's cheaper to use a belt than a chain, it will last beyond the warranty period, and most (not all) people who buy new cars will trade it in for another new car before the timing belt becomes an issue. People who buy used cars are used to (and should expect to) buying trouble in a proportionate amount to the mileage - if I buy a used car with 75K miles on it I expect some things need fixing, if I buy a car with 125K miles on it I also buy a 6-pack of duct tape. I've had cars where the engine lasts longer than the body, so when it looks that bad, who would want to drive it?
I had a timing belt break on a Dodge Caravon/3.0L 6cyl Mitsu engine. Two incredibly ironic twists - first, it happened while I was driving to work, a light mist in the air, and I was thinking how nice and smooth the engine was running when it suddenly just stopped running. The second irony - I didn't want to do the repair myself, so I had a shop do it. I had just gotten a state tax refund check 2 days earlier. The repair cost exactly what the refund check was to the dollar (not the pennies). I don' remember the exact numbers now, but something like refund check $468.86, repair cost $468.12. Easy come, easy go!
Currently rebuilding a 1993 Plymouth Sundance Duster with the same engine, a Mitsu 3.0L V6. What a cool and fun little car!