Thank you for an interesting question with a lot of different views. In this unforeseeable situation, it’s difficult to say “to kill” or “not to kill”, it’s a case by case basis. And if it is “to kill”, I agree with some of you that when the market is not lucrative and supportive, the project is not fully “killed” but maybe hold off till a later time or change priority. Killing a project should only be the last resort when faced with seemingly insurmountable obstacles.
I think killing a project midway would make sense if for example the technology used is out of date/there is something new coming out that is absolutely better then changing the project is a better idea than investing in dying technology.

I don’t think killing a project midway make sense 100% if the product is just out of fashion, or marketplace being unattractive, the products can still have a chance to become successful or even shift the market if the products are exceptional.