Because any work delivered in such circumstances has no value (it might be done by your friend for all I know). It creates incentive for candidates to waste tim

Because any work delivered in such circumstances has no value (it might be done by your friend for all I know). It creates incentive for candidates to waste time polishing the solution. Most importantly, if you are an employer, think you are probably turning away your best candidates as the only ones that will continue are the ones that are OK with this b*t. Maybe they don't know any better or don't have other concurrent offers to work on or they don't have current job or are not putting effort at the current one. In any case it is likely that they are not your best candidate unless you are best employer in the world that they will do anything to work for. Funny thing, best employers in the world don't ask candidates to do home assignments. If I am on the market I want to find and chase some number of potential offers. Ideally, I will get all those offers at the same time to pick and choose the best of the pack. This all happens while I have other engagements with my current employer, while I am closing projects, etc. I don't have infinite amount of time. A request like that would drain all my available resources and prevent me from taking part in other processes.