My grandfather has been like that for over 10 years now. It's not always Alzheimers, because that is accompanies by a slew of other symptoms that my grandpa thankfully does not have.
It just means the person's brain is deteriorating. It's true that there is nothing that can be done to reverse this, unfortunately. You and your family will have to live with it. There are certain things that can be done to make it easier for everyone, such as trying to find the affected person a routine, or a repetitive activity to keep them and their brain busy.
I have heard that Ronal Reagan, who became very forgetful near the end of his life, would constantly clean the swimming pool in the backyard. The family would apparently rethrow all the leaves in the pool when he's done just so he can get back to it.
Not sure that's the best remedy but any physical or mental activitiy can help.