That seems to be jumping the gun. You don't normally get an onsite immediately, you usually have to go through much shorter screens, the first of which may only be an hour max. So you don't necessarily waste a lot of time on any one company unless you go deep into the process, and you're probably going to be screened out early by lot of them. The take home assignments are generally supposed to be replacements for technical screens, but they invariably take a much longer amount of time.

There's also an investment differential. Every hour that a candidate has to spend in an interview is also an hour the employer has to spend in the interview. Whereas an employer can send you off with a take home project for an indefinite number of hours while they sit back and do nothing. Are they going to spend the same amount of time reviewing the project as the candidate did writing it? Extremely doubtful.