Three points

Firstly, if Madara did it no reason not think that Obito just did that too and will be waking up soon.

Secondly, someone give Hashirama a Sharingan to sort this whole mess out.

Thirdly, the Jyuubi is yet to undergo its final transformation. It could be that this is why the SotSP sealed away his mother, because she could not longer control the Jyuubi in its final form.