Every previous adoption of technology has taken - what, 50 years? - between having the technology and being set up to make use of it. Gasoline did not immediately have car engines to put into, nor kerosine a whole city's worth of lamps set up to receive them, etc.

Though at first, if fusion could power up the existing electrical grid then it could e.g. make electrical cars more efficient in the net/overall sense, even if vehicles operating directly on fusion power themselves would take many more years. So fusion really might be different than those that came before, if we are anticipating and more ready for it than previous technical advances?

Though yeah, it will have its own challenges e.g. the radioactive wastes, so fusion would not begin to replace greener energy approaches such as solar, wind, and geothermal, only perhaps supplement them.