Because whenever it's even vaguely cold outside, my neighbor likes to be able to start and idle her giant truck in her driveway without leaving her house (for 40 minutes before she drives a mile to work).
Unfortunately, after market remote starter does not offer this capability, so with the new trend of monthly charges, if you like certain brands like Toyota, and you want that type of secure remote start, you have to pay $20 per month or more for the life of the car.