It could be that BB just sent some of his Titanic Captains to get it, similar to how Burgess went to Dressrosa. Melo Melo no mi is a useful DF similar to how Mera Mera no mi is useful.
BB wants all "strong" DFs, so him going after Hancock's DF itself is not a problem. The problem is that we thought BB was going after something much more important and impactful.
I blame Oda for baiting. This is not what I had in mind when BB said he would rather take it than letting Marines take it.
But if Melo Melo no mi is another secret God DF like Luffy's,
@AverageNamiEnjoyer and
@OnePiss should start counting their days.