The reason for invert is EVERY stage inverts.
Actually every stage with voltage gain inverts. To have a non-inverting preamp with gain you need at least two stages of voltage gain.. an inversion and another inversion puts you back to non-inverted. In almost all cases you can get enough gain from a single stage so CJ and others choose a single gain stage followed by a buffer stage that does not invert. Why add a buffer? By it's nature a voltage gain stage has an output impedance that is too high so the buffer lowers the output impedance, has unity gain, and does not invert. Net result.. voltage gain inversion followed by buffer non-inversion = inversion.
Since you can correct for the inversion by reversing the speaker cables why add another gain stage that isn't needed?
Don't most good preamps have a polarity reversal switch?
In a perfect world they would but adding that feature means some additional circuitry that some feel degrades performance.