It's an employer's market. Why would an employer want to wait 3-4 weeks for someone to interview elsewhere when there's a dozen other candidates in the pipeline?

In reality people are trying to put food on their table and they will spend the entire weekend polishing their submission. If you don't follow suit your submission is going to look comparatively bad.

It is different than traveling to a different city for an onsite because you're not wasting your teams time on a candidate unless you think they have a good chance of getting to the end. You have "skin in the game" as they say.

If hiring managers were only issuing homework to candidates already scheduled for a full round of interviews, so interviewers have standardized material to talk about and as a substitute for whiteboarding, it wouldn't be so bad. Instead you mostly get nothing to show for your time and when you do get a round of interviews nobody looks at what you did and wants you to do medium+hard leetcode on the shared screen.

Ideally yeah but does it ever take "only" 4 hours? Usually take-homes are pretty unguided and leave room for personalization, plus there's an element of pressure to them to make it "awesome," do all of the best practices, etc. At least with a pair coding session there's someone there setting the guard rails to keep you within 1h.