bringing in care taker managers presents it's own problems, especially you are looking to install a long term successor, it is much easier for that successor to come in after the failure of a previous manager, and all the good will that brings and time it buys them to do that job. Ironically the caretaker having success can actually hinder long term plans, and in some cases throw those plans completely out of the window, and in exchange for short term success (some will argue it's worth it), you comprise a long term plan and might actually set the club back, some examples off the top of my head, Stuart Lancaster, Tim Sherwood and Di Matteo (the champs league quite possibly being worth it!)