We didn’t have a steampunk society at the time the transistor was invented. We were already post-steam with internal combustion engines dominating the vehicle market, including on rails with diesel-electric locomotives (diesel-powered internal combustion generator that produces electricity to run electric motors in the wheels).

The problem with steam is that it’s highly corrosive. High temperature boilers and steam parts and fittings require a lot of expensive maintenance to repair pinhole leaks that cause loss of steam power and pressure. Internal combustion engines don’t have this problem because they keep the heat contained inside the engine cylinders which are surrounded by a jacket of constantly circulating water-based coolant (that sheds heat through the radiator). The useful power that leaves the engine is purely mechanical, transmitted into the crankshaft and then the transmission and driveshaft. These parts are lubricated with oil and low maintenance due to the low temperatures and low friction of the system.