Because they follow the Lunar Calendar.
they celebrate CHINESE NEW YEAR
they are different because they are really celebrated by different types of people and they have different gods and celebrate it in a different way...
people celebrate Chinese new year is because Chinese new year is their tradition.
we celebrate it in different days in the years
83 percent of Chinese celebrate Chinese new year
They celebrate at home together with their families
Chinese people celebrate Chinese new year because it is a brand new year for Chinese people (and they want to receive red packets).
Chinese celebrate Chinese New Year, Moon Cake, and Lantern festival.
It is the new year based on the Chinese traditional calendar, like the new year we celebrate on 1st January every year, only on a different date.
It's the same reason that people celebrate Easter or Christmas: it is their tradition. If you are Chinese or are interested in Chinese culture/traditions, you may celebrate Chinese New Year. It is just like westerners celebrating our new year except the Chinese choose to use a different date.
Chinese
Different religions and cultures celebrate different new years. For example, Chinese New Year is different from Jewish New Year, and both are different from the new year of the Western calendar in which New Year's Day is January 1.