Your approach doesn't save any time or effort for the hiring company though. It's the in depth interviews that take up so much time.
You may not like it but this is their motivator, not being nice
You're right. I don't like it because what you're describing is generally how shitty companies operate. Often they won't even look at the coding test. Those companies deserve to get the worst of the worst candidates that they're optimizing for. They fit into the category above: nothing of value to offer the candidate.
If I spend two hours coding some toy project, I expect the company to spend two hours talking to me. Either interviewing or constructive feedback relating to their rejection.
A company that wastes 1000 people's hours and then ghosts 990 of them should be embargoed by some kind of a computing and technology service workers' union. (You know... the folks who can herd CaTS.)
If the company feels justified in wasting a lot of your time in order to save a little of theirs, before the interviews even start, imagine what they will do after hiring.