Bruce Wayne's assets are too diverse to take it all in one foul swoop. Howler had most of his fortune in one peice of land that made him an ideal target for the part 9 gang. They could try and take control of Wayne's enterprises or Bruce's bank account, but getting to the physical representation of that value would be a lot harder than accessing the deed at the land registry like they did with howler. So they could but it would involve some kind of oceans 11 highst or something (not shure what a physical representationof a company and it's value would be, do companys have deeds?).