Why aren't Cancers and Virgos compatible?

Much like with anything there are good points as well as bad points. With Cancer (a water sign) and Virgo ( an earth sign) we find mostly a positive match. They are both negative polarity and feminine. Virgo is the least known of the duality signs (Gemini is the best known, Pisces is also well known and Sagittarius is lesser known like Virgo) and one can expect to fine a hidden side to the Virgo personality. Virgo's are know to be very clean and organized but look into their bed room dresser drawers and you'll often fined a mess hidden from view. Cancers tend to be emotional (water) and home bodies which fits in well with Virgos hard work ethics. The cancer person can help the Virgo person expand their narrow views and the Virgo (earth) can help the Cancer person to be more grounded and practical; of course like all things these can also lead to disagreements and arguments if the two people don't trust one another.

This is all based on Sun sign Astrology and is limited in scope based on only the sun position. where other factors such as Moon, Venus, Mars, as well as the houses they occupy; one would also like to evaluate the ascendent / descendent (1st (self) and 7th (partner) houses and the 5th house (romance and children) and any aspects made to these planets and houses in each horoscope as well as viewing each persons horoscope to see how these fit together.

So you can see for a truthful answer much more information is needed. Sun (personality) sign astrology does work but only in a general sense. And astrologers as a whole like Doctors and mechanics are only as good as their ability to understand their craft.