Why was Napoleon exiled rather than executed?

Surprisingly, there was no question of executing Napoleon’s following his first abdication in 1814 as it was subject to certain conditions laid out in the Treaty of Fontainebleau. The treaty contained some 21 articles but among the more important ones, the island of Elba was made a sovereign principality, separate from France and Napoleon it’s emperor. Napoleon was also to be granted an annuity by France of some 2,000,000 francs and various other members of his family other amounts.