Because its an efficient operating model. The taxi operating companies negotiate good fleet prices on stripped down cars from the manufacturers and rent them out to the drivers for S$90 a day (or around S$150 a day for the limo cabs). Taxi utilisation in Singapore is relatively high, and the average driver collects S$300 for a 10-hour shift, which means they clear around S$150 a day after costs, often more because many taxis are driven by 2 drivers in 2 shifts, splitting the rent. Average taxi driver monthly income (after costs) is S$4k-6k a month, which is a decent wage for Singapore.

Is it a hard life for the drivers? Sure. Do they work for nothing to survive? No.