User blog comment:Plainblack/Luffy's Handicap/@comment-94.68.165.51-20130329202058

Doflamingo Family seems to not know what fruit Luffy has, most likely most of the villains he has met so far.

If there is a reason to hide his DF abilities, is because most of the competitors are expected to be no DF users and they aim to become one by winning the tournament. But still, it's easy to explain why a DF user want to get Mera Mera no MI, even as an investment this fruit worths it.