Since the decision to disfellowship is arbitary then the decision to reinstate can be equally so. Elders use reinstatement as part of a power trip making the person jump through hoops so that they will be totally cowed by the time they are allowed back in.
The decision to delay could depend on many factors such as: the nature of the original offence, whether an elder or a member of an elders family were involved, whether the elders liked the person originally, how widely the original offense was known about, a megalomanic elder who just wants to be a hard arse.
If it involved a marriage break up and a husband or ex husband is still an elder then they can make things difficult.
My advice to them is don't bother with them educate yourself and build a life outside they are not worth the effort.