Why are figure like Lenin and Nepoleon exiled from their countries instead of just straight up shot for their crimes?

As the case of Napoleon I has been well addressed in the response by u/kieslowskifan referenced below, I'll just limit my reply to the Lenin's case.

Lenin couldn't have 'just been shot' because Russian Empire in 1890's was, all things considered, a state of law and political sedition that did not include terrorism or plot against the life of the ruling family was a crime punishable with and exile, usually carried out in an administrative mode. It should be noted 19th century Russia the exile was actually more a forced relocation to a secluded location, usually in southern Siberia, so that the potential political troublemakers, moved from large cities to small towns or villages were unable to continue their activism on any significant scale. The carrying of the sentence was usually less strict than regular imprisonment, as the sentenced were allowed some time (few days or, rarely, weeks) to attend to their personal and professional matters, meet the family, make necessary administrative works (ceding ownership or giving instructions in case of entrepreneurs, making official last will and testament in notary office etc.) and were obliged to arrive at a specific location they were transported from (what worked more or less like the bail in an American justice system). Please note however, that I'm using the word 'sentenced' in the wide sense because, although the punishment was usually quite lenient (at least since the Spyeranski's reforms introduced in 1822, because earlier the exile to Siberia was usually lifelong), they could have imposed by a court verdict or the administrative decision (for comparative purposes, administrative punishment is e.g. speeding ticket issued by executive officers with no court involvement). I'm mentioning that because Lenin himself had been exiled in the latter mode. On the other hand, the period of such exile was 1 to 5 years according to the Act of crime prevention and suppression issued in 1890.

Summing it up, Lenin was exiled for three years to a Siberian village in Krasnoyarsk Land because in 1897 this was the punishment for his actions as stated in the Russian penal code.