Beyond the cost issue mentioned by others, the exercise element that you mention is maybe more important than you think - older folk often fare better if they can stay active, and this might be a subtle way to provide that.
Also there's the physical size - 80cm x 80cm - retrofitting an elevator into a small property has some serious space demands.
>older folk often fare better if they can stay active
I can directly vouch for that, in an anecdotal way. My mother, in her last months, fought through immense pain to do her daily activities. After a four day stay in the hospital for a heart-related issue, she was never able to walk unassisted again.
