The difference here is that a machine--engines--are easily subject to breakdowns, repairs no longer working, updates going through paces before functioning properly. Jedi are not machines--their power is as much a part of their makeup as their organs, so the use of this power by trained individuals should not suffer from highs and lows, forgotten skills, etc.
I understand what your saying but for example in Star Trek how could they forget they have transporter arm bands as a way to exit an emergency situation in one episode but 2 later not bring them?
I could provide you many other examples in Trek where an engineering plot device is used only forgotten about. In Wars Jedi strength is no different.