The mafia won't benefit as much from a spider member dead but not in their possession. In that case they couldn't even be sure the target is truly dead, and thus couldn't spread the message this is what happens if you screw with us or they can't torture a living captive they don't have for information. Plus the big bosses won't believe until they get the corpse, which they wouldn't get before paying. Like I said earlier, they can't simply claim the body (or even a living target) from somebody who is stronger than the target they couldn't take down in the first place.
All this led me to believe the whole five million wasn't there originally but somebody just decided to make some cash in the middle.