I think the change was needed in order to bring some stability of mindset if nothing else.
I like Unsworth but a lot of his words were empty and almost cliche. Bringing Allardyce brings calmness because, undoubtedly, he secures sides.
Carrying on with Unsworth or bringing in Silva, they bring with them risk. Whilst you can never say never in football, hiring Allardyce is about as secure as you can get.
I suspect he's also been brought in as a hatchett man, with a free reign to bin a load of the dead wood off. ( hopefully in readiness for whoever takes over in the Summer. )
I should imagine it would've been very difficult for Unsworth to bin off the likes of Baines and Jageilka, due to his long term ties to the club.