Why do they name only 44 presidents?

I am not sure what you want to know. Elections occur every 4 years, starting in 1788. Some presidents are elected twice. One(F D Roosevelt) was elected to four terms. Four presidents were shot and killed, four died of natural causes, and one resigned without finishing his last term. Grover Cleveland was president on two non-consecutive occasions, and so is counted twice (as the 22nd and 24th president). Obama is the 44th president, but is really only the 43rd person to occupy that position.