Back when I was working for a company that did take home challenges, those who passed had their challenge as the topic of conversation for the final interview. For those who didn't, I gave written feedback, at least a page if not two.
My thinking was if someone took time to give me something, they deserved something in return, even if it wasn't a job.
If you have not been through the process you may not truly understand how nice (and rare) your thought process is.
Sadly I have chased up situations like that only to get told "you provided one of the strongest pieces of work, however, we decided not to proceed to interview" - or responding at all apparently.
My thinking was if someone took time to give me something, they deserved something in return, even if it wasn't a job.