[ Because, at the time, it had been the only solution given. The only one presented. Vanitas still continues to believe that the best option - his only option - is to have someone tied directly to his heart. Honestly it's been working. Or, rather, had been working... ]

Not that any of you would let me anyway.

[ So there's really no need to pursue it. Not that Vanitas would because he already knows it's futile. Ventus' heart is mostly healed so... ]

And the solution there was still to tie myself to others. There doesn't seem to be any other way.