People use it for lower-grade hardware that they are still manufacturing today. Go buy a $39 "unlocked" phone at your local Fry's (search for a brand like Blu). What will it be running? Android 2.3. Which is wonderful.
That is one end of the scale, yes it is good that you can get a cheap device running an old OS but you have to remember this is unsupported and quite insecure. If you're ok with that then that's fine but again, that's only one end of the scale.
How would any user buying it know? Does it say "beware, running unsupported 5 year old phone OS, buy at your own risk" ?? Does it not have warranty? If it has warranty, is it not supported?