System of the Aeolipile Heron Steam device from Alexandria 10-70 AD
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It was lack of steel to make pressure vessels (boilers).
As opposed to increased pressure like a steam engine's boiler, Hero's device operated by condensing steam and producing a vacuum. Thus the maximum pressure differential it could create was 1 atmosphere: 14 psi.
You could do some work with this - mostly using it for the vacuum, sucking up water and whatnot. For other applications animal energy or waterwheels could outcompete this sort of available work.
A steam locomotive operates under pressures of 200+ psi. It can easily outcompete animal power and does not need a specific fixed site like a waterwheel. The Romans had iron but for a boiler that can withstand that sort of pressure you need steel, which was the innovation that made steam engines possible.
An Aeolipile is Very Inefficient
In addition to what Will said about manufacturing difficulties, such devices are not used in modern times because it can't compete with the power generation capabilities of a turbine. Both operate using the Rankine cycle which entails heating a working fluid (water) into steam, having it do work (turning a generator), cooling the fluid and re-pressurizing then repeating the process. The Aeolipile wasn't exactly a closed system, but it operated in a similar fashion.
A turbine has fins along its length that are optimized to extract as much energy as possible from the steam as it expands through the system. Turbines can also operate at extremely high pressures which increase output.
The Aeolipile has steam running through nozzles to set it spinning which wastes energy because the steam still expands once it exits the system which is wasted work. Additionally, you are limited on how fast the system can spin due to drag. Higher pressure will allow the system to spin faster but at the cost of wasting more energy in the expanding steam and greater drag because the force of drag goes up with speed.