Pilot Project
I think because it's nicer than bus service. You ride in new, modern cars, not utilitarian buses that have changed little in 50 years. Cars have become much quieter, more comfortable, and more reliable over this period. Buses have not. By not improving the mass transit experience to match, Metro Transit lost its middle-class business.
Now, we could address the latter without a mulit-billion dollar Central Corridor light rail system as is proposed. Assuming mass transit usage is truly your goal, how about upgrading the buses?
We could start with a pilot project. Purchase a few upscale buses with soft seats, sound insulation, even heating and cooling, cup holders, tinted windows, maybe a little music. Make limited stops, but make a wide loop through each downtown. Provide enough slack to ensure reliable, on-time service. Charge $5 a ride, $10 for first class with fold-out desks, power and internet service for your laptop.
If there is some great unmet need that will attract riders to a light rail system, this will find most of them.