[ryao]

They are dependent on Apple for updates due to the code signing. Alternative operating systems also cannot be installed once Apple stops supporting them. That ensures obsolensce in the long term, even if it is longer term than their competitors' blob-ridden Android products.

Anyway, plenty of machines sold then and even today are junk, so maybe replacing them is not such a terrible idea. However, I think replacing the software matters more. Linux is an excellent option for these systems in the long term. If Apple made Mac OS X available for them, it would be too.