While the engines might be power efficient they might not provide enough thrust for rapid takeoff required for real rockets who don't have antigravity and magic. The economics of flight changes to favor space efficient over atmospheric and likely a lack of launch specialized engines. That being said I am sure there are spaceports that provide use of booster rockets or electromagnetic catapults for inpatient paying customers.
"To achieve orbit, the shuttle must accelerate from zero to a speed of almost 28,968 kilometers per hour (18,000 miles per hour), a speed nine times as fast as the average rifle bullet.
To travel that fast, it must reach an altitude above most of Earth's atmosphere so that friction with the air will not slow it down or overheat it. The journey starts relatively slowly: at liftoff, the shuttle weighs more than 2.04 million kilograms (4.5 million pounds) and it takes eight seconds for the engines and boosters to accelerate the ship to 161 kilometers per hour (100 mph.) But by the time the first minute has passed, the shuttle is traveling more than 1,609 kilometers per hour (1,000 mph) and it has already consumed more than one and a half million pounds of fuel." https://spaceflight.nasa.gov/shuttle/reference/basics/launch.html