Why one car
The conventional wisdom in this trade is fleet: more vehicles, more bookings absorbed, higher utilisation. OSPIPO is deliberately the inverse.
What passengers here are actually paying for is not the badge on the bonnet. It is recurrence. The person who collected you from Tuesday's Singapore flight is the person collecting you the Tuesday after next. The route is remembered. The preferred terminal, the preferred coffee stop, the preferred quiet — none of it has to be explained twice.
The cost of that is honest and worth stating: there is one car, so there is a diary, and sometimes the answer is that it is already somewhere else. The fare engine on this site shows real availability rather than implying there is always another vehicle.