Because air conditioning was rare and they melted. He saw a machine pharmacies used to make pills that were round and wafer-shaped, and thought he'd use those to make mints, which at the time were made square (because they were pressed in sheets and then sliced into squares). The machinery could also punch a hole in the center, and Crane named the candy after its resulting life preserver shape.
In 1913, Crane sold the formula for his Life Savers candy to Edward Noble of Gouverneur, New York for $2,900. Noble started his own candy company and began producing and selling the mints known as Pep-O-Mint Life Savers. He also began to package the mints into rolls wrapped in tin foil to keep them from going stale. This process was done by hand until 1919 when machinery was developed by Edward Noble's brother, Robert Peckham Noble, to streamline the process.