Few cars isn't no cars.

Returns are a little unpredictable. You've never dropped off a car ten hours early, nor kept it a day longer without calling?

In 30+ years of rentals I have been in a situation with no cars exactly once - immediately post 9/11. In a few - and I mean a few - situations I have waited for the reserved car type.

Algorithms that predicted car shortages down to the last <4 vehicles would prove inaccurate at large, busy stations. Text alerts would cause needless anxiety.