There's a difference between can't and shouldn't. It's the latter in this case.
I won't go on since this is just getting into semantics now.
Pretty sure it's because no one knows how Ichigo's bankai worked(/works). They said the one stealing it needs to know how it works and be powerful enough to steal it, if I recall.
And to be honest, we have no idea if he still has his hollow powers or not. Right?