Answered a similar question below. It's equally crazy to me that people wouldn't immediately understand the elderly having quality of life issues.

A few that came to mind: -chronic pain -immobility (walkers/wheelchairs etc) -mental decline (senility) -loneliness as you say (possibly addressed by mental decline but it's often cited as a major issue for the elderly) -exponential medical costs

There's probably a lot of other reasons as well I'm sure. What a drag it is getting old.