It only takes me a few days to get stronger, but it takes me months to lose that strength.
Strength lingers, in case you need the abilities again at a later time.
One really don't need to train that often.
It's better to train some times each week, but vary the exercises as much as possible. Legs you can train more often and mostly the same way because it is also good cardio.
This is the optimal and complete knowledge to train the best. That's it.