[inigyou]

Because they are people who make trains. The people who own farms think about making solar fields. The people who own roads think about making solar roadways. The peo who make trains think about making solar trains. All of these possibilities can be trialed in parallel by different people. It is the same reason that if asked to design a combination lock safe, you would probably reach for a microcontroller and a keypad instead of a bucket of gears, because you are (I presume) a software person and the hardware people can try the other way.