these are altcoins and altcoins are being created every day.
the reason for it is because it is easy to create one, specially when you are forking an existing cryptocurrency which is practically copy pasting the code (which is open source and free to use) and creating your own coin.
the purpose of them is to make money! most of these have added a premine to their coin which means as soon as the new blocks on that altcoin (the forked coin) started being created the developer got his hands on a large number of his own coin which then he could dump on the market and make a large amount of money out of thin air.