Why does Nokia need another OS?

I was going to add it to my original post in the Tribe but it is more specific.....

People keep saying that they need another OS and that Asha wasn't cutting it and they can only do so much for WIndows phone?

How does that argument work exactly if they are selling their Devices division to Microsoft so why does Nokia NEED another OS to replace Asha if they are in fact selling Asha to Microsoft? Now in the off chance the deal somehow fell through(that'd be catastrophic and i can only imagine then a Lumia 1520 inspired X device...which then means I would probably drop them altogether and head right to iPhone LOL) and this was something they released afterwards but i am curious as to why people feel Nokia needs another OS because "Windows Phone is selling and asha is....and this is meant to replace Asha" when they are essentially about to give up their device team?