Did your ancestor include several codicils to his or her will, making specific changes or additions, but not desiring to go to the expense of completely revising the entire document? Those codicils may tell a story.
One ancestor had four codicils to his will. All relate only to the inheritance to his daughter. Originally she is given a cash amount from her father's estate. Later it is stipulated that her inheritance is not to go to pay her husband's debts. Later it is to be put in trust for her and money to be set aside for her children. Finally a trustee is appointed to oversee the inheritance which is to go to the daughter's two daughters.
What is unstated is significant. The son-in-law has serious financial troubles, eventually committing suicide. The daughter becomes ill and leaves her two surviving daughters in their teens. The grandfather survives this deceased daughter and the changes in his will are an apparent reaction to the son-in-law's financial difficulties and to the deaths of the son-in-law and daughter.
Of course, all the reasons are not stated in the codicils--sometimes the researcher must look behind the scenes.