Engines are constantly evolving and becoming more powerful, sometimes at the expense of driver safety. Controlling the speed of a turbocharged car is as simple as reducing the turbo's boost. Turbocharged race engines are less expensive, and more reliable. Also, turbocharged engines don't have to rely on exotic, expensive materials to reduce reciprocating mass . As naturally-aspirated engines become larger to increase power, the stress due to the necessary increase in engine RMP and increased reciprocating mass placed on their various components also increases.
Turbocharged engines are quieter.
The turbocharger on an engine acts as a natural muffler, minimizing engine noise and providing a more spectator-friendly environment at the races.