After decades, why does Old-Age-Makeup still look so terrible?

The film industry has been at it for almost a century, and still they seem to be unable to create believable old-age-makeup.
I just watched a (free) stream of kapitän amerika 2 and there was a scene where he talked to his old girl friend, who is now 300 years old. Apparently, instead of getting an actual old woman to play the part, they put old-age-makeup on her and even “enhanced” it with cgi.
And it just looks laughably bad.
The same is true of old Weyland in Prometheus.
I do not know a single movie where the old-age-makeup looked good or even approached realism.
In an age where they can make cgi monkeys look real, why do they still fail so utterly when trying make a human look old?