Yes, the amount of effort it takes to care for someone with dementia and/or mobility issues is huge. You end up needing a full time care giver to either keep them from wandering away or taking them to the bathroom and feeding them 5-10 times a day. Doing that in a humane fashion is quite challenging... and at some point you realize it's largely for their surviving relatives.

In the old days we just let them wander off or wallow in bed until they died.