Is it something we’ve bred into them?
Do wild fowl do that?
Would a one-egg bird like an ostrich waste time incubating an unfertilized egg?
Yes, wild birds sometimes by accident produce unfertilized eggs. However, the penchant of domestic chickens to do so routinely is something we have bred into them.
Birds may sit on unfertilized or otherwise “bad” eggs indefinitely. In conservation progams for endangered species, those who are monitoring nests will often check eggs to make sure they have been fertilized (by candling), and remove those that are no good to ensure the birds re-lay.
Ostriches, by the way, lay many eggs per clutch.
I thought it was something to do with the cock not being allowed to play mummies and daddies with the chickens… 
NO ROOSTER(S)!
Ask an ostrich.
The reproductive system of chickens has a sort of ‘inertia’ to it; the egg has to be produced in advance of fertilisation anyway and the whole system is geared up to crank out eggs on the assumption that there will be a cock available to fertilise them.
The rate and sustainability of production might be higher than in the wild though.