Because if you use this() and super() together in a constructor it will give compile time error. Because this() and super() must be the first executable statement. If you write this() first than super() will become the second statement and vice-versa. That’s why we can’t use this() and super() together.
For More Information Please Refer: https://stackoverflow.com/questions/10381244/why-cant-this-and-super-both-be-used-together-in-a-constructor