There's nothing strange about how often this error is repeated. It is a fault in the "design" of the English language, which violates its own rules, insofar as it has any. Apostrophes are used for both possessives and contractions, eg. "That's John's ball". Indeed possessive "it's" was historically written with the apostrophe. That the apostrophe was dropped to become possessive "its" is completely arbitrary special-case logic, and given that there is no logic behind which it was dropped from, it is easily subject to confusion because you cannot reason about which is which if you forget in the moment.