'They're not the drastic life-saving measure some people consider them to be.'
No one is saying they are. The main issue is and should always be that this individual is in an advanced-state of dementia. This person's brain is already very damaged, it will not improve with time, only worsen, and depending on how far advanced it is and the speed with which is it progressing it can indicative of the need for DNR but again, the issue is that this was not discussed with the family.
Again, DNR is and should be about quality of death, which is a part of life, IMO, for individuals for whom death is an event which is a certainty in the near future and who may have other significant health issues relating to their condition and it should, as edam suggests, be a legal requirement for doctors to discuss this with the patient and their family or make suitable attempts to do so and record them.
When you get to the stage of DNR it involves the patient's quality of life as pertains to how they will meet death because such patients are so ill the only way they will go is down, not stable, not even, but near enough to death for this to be a relevant and important discussion.
That's why many families sign such orders on behalf of relatives who are no longer able to do so or children with terminal illnesses whose health has been so severely weakened by their condition and its treatment that the only question about the quality of their lives is do they die on a vent in a PICU, or die crashing during the vent process, or throw a clot or other complication from mechanical intervention that is traumatic and awful, or do you make provision for them to die peacefully surrounded by those they love and who cared for them.
But it's something that should be discussed with family and the patient, if possible, and their doctors.