This has been asked here a few times before. While you wait for a response, you may be interested in these older answers:

https://www.reddit.com/r/AskHistorians/comments/3r6qy0/why_was_napoleon_exiled_rather_than_executed/

https://www.reddit.com/r/AskHistorians/comments/4azxn5/why_was_napoleon_exiled_to_elba/

https://www.reddit.com/r/AskHistorians/comments/3n6tbl/how_did_napoleon_bonaparte_live_out_his_days_in/

https://www.reddit.com/r/AskHistorians/comments/un6z4/why_was_napoleon_bonaparte_exiled_twice_instead/