Equipment which costs less is more likely to be available. But cost is not the sole or even primary determinant. If some technology meets the other criteria described below, it will be made widely available despite the cost. One thing which makes the telephone useful is that we do not need to boot up the operating system before we make a call. Electrical lights are a significant improvement over systems which required individual ignition with a match or candle.
Streetlights are practical because they turn on when it gets dark outside.
Much of today's educational technology requires long and sometimes cumbersome initialization procedures. After wheeling in a projector from another room, for example, three teachers and a technician may spend time plugging it in, turning it on, spooling the film, and positioning the screen. This requirement has significant energy consumption considerations. A portable device, for example, cannot always be on, because it must carry its own power supply. Good technology is always connected.