Is there something peculiar about this particular star cluster?  Some astronomers have considered such a notion although may not be sure yet on the cause:

This is particularly odd as it is known that most stars are born in such clusters. Astronomers have wondered if there might be something different about planet formation in star clusters to explain this strange lack.

This cluster lies about 2500 light-years away in the constellation of Cancer (The Crab) and contains about 500 stars. Many of the cluster stars are fainter than those normally targeted for exoplanet searches. Of three new planets, two are orbiting stars similar to the Sun and one is orbiting a more massive and evolved red giant star. The first two planets both have about one third the mass of Jupiter and orbit their host stars in seven and five days respectively. The third planet takes 122 days to orbit its host and is more massive than Jupiter.

Do you have any thoughts on this unusual place where they found planets?  Feel free to comment with your theories.