The Aeolipile was not a functional steam engine - it was essentially an unpressurised two-spouted kettle that span on an axle. It had no way of maintaining enough pressure (no valves) to do useful work and the metal working techniques of the day weren't good enough to contain useful pressure without exploding. Real steam engines only came about after people had spent centuries building cannons that didn't explode.
The first practical application of steam engines was pumping water out of deep coal mines (which the Romans didn't have or need) where it didn't matter if the engine was both underpowered and massive. Even after these engines became commercially viable, it took another 70 years or so for the engines to become small enough to be mounted on vehicles.