Why wright code like that

Question

The code in this excercise is:
words = ["Python", "fun"]
index = 1
words.insert(index, "is")
print(words)

but why not this?:
words = ["Python", "fun"]
words.insert(1, "is")
print(words)

Answer 1

To make it more complicated? (to show you that you can use vars in args of method?)