Trying to imprison the guy leaving office is a great way to have that guy not leave office. There's a reason that presidents don't get prosecuted, and it's not because nothing illegal happens.
It's like trying to end the war in Ukraine while also saying that you're trying to depose Putin. Putting very powerful people in corners tends to be a really bad plan.
I don't know if it is such an easy answer. On the one hand, a policy of not prosecuting the office holder might help the peaceful transfer of power; on the other, such a policy creates an unaccountable sovereign every four years.
Was it fear of prosecution that kept Caesar from giving up imperium when returning from Gaul? It was certainly a factor. Would there have been no Roman civil war if there was such a non-prosecution policy in place? I'm less certain.
The risk you bring up must be carefully considered, but so is having an unaccountable sovereign, just four years at a time.
It's like trying to end the war in Ukraine while also saying that you're trying to depose Putin. Putting very powerful people in corners tends to be a really bad plan.