People are not generally allowed to cut spouse off from inheritance.
It is not a simple matter to disinherit your spouse, according to the Times Herald-Record in "A spouse's inheritance rights no simple matter."
The details vary by state, but a surviving spouse has the right to make what is known as a "spousal election." This allows a spouse to elect to receive whatever is or is not given to her in the estate plan or to receive a certain percentage of the total assets of the estate. Commonly, this election is for between one-third and one-half in most states.
The reason for the rule is that people felt there was a duty to care for one's own spouse and that it would be wrong to leave a widow destitute.
There are ways around the law, if the spouses have entered a pre-nuptial agreement, but they are not ironclad.
An estate planning attorney can advise you on circumstances that may arise for a surviving spouse, as well as creating an estate plan that fits your unique circumstances.
Reference: Times Herald-Record (Aug. 31, 2017) "A spouse's inheritance rights no simple matter."