I think that the mistake is common because it is triggered by a language irregularity. Normally in English, 's indicates a possessive. By that logic, something that belongs to "it" should be "it's", just as something that belongs to John is "John's". But no, we spell the possessive pronoun "its".

And I've often seen autocorrect try to turn a correct "its" into an incorrect "it's" or vice versa.