My reasons:
Because Coach doesn't even recommend their own products on many of their bags (Madison line, legacy, etc.).
And because Coach products have silicone so the leather cannot breathe and future moisture cannot properly get to the leather.
Most brands are better than Coach moisturizer, Apple being one of the best (especially for the price... there are higher end products like Loving my Bags which is supposed to be good, but too pricey for me). The apple moisturizer is also a gentle cleaner, so it moisturizes while it cleans. I do not use Apple cleaner and heard good and bag things about it.