The sentence would not read well with a comma. It would be an example of the error known as "comma splice": that's why it should be a colon not a semicolon.
Naw, the “it” in the 2nd clause is referring to the first clause, and they are directly related. They are not independent unrelated clauses, and that’s the criteria for a comma splice. Your assertion that a colon should be used contradicts the idea that using a comma would make it a comma splice error.
In this case, this sentence’s meaning and point would get across unambiguously no matter what punctuation is used between comma, period, colon or semicolon. What else matters?