I am building a product/startup [1] to address some of the problems you mention, and as a result, I've been talking to hiring teams at several companies, so I can give you some reasons why the processes are bad.

* Hiring is a marketplace, and supply/demand is not always balanced, so most issues related to job search/hiring is due to this.

* When a company posts an ad for a job, they usually receive about 150-200 applicants within 2 weeks, thanks to job boards, LinkedIn etc. Unless it is for specific high-skilled jobs, in which case, they receive hardly any applicants at all.

* Most of the applicants are usually not a match for the job, but given the number of applicants, recruiters rely on resumes, social profiles etc to shortlist about 20 applicants.

* Tests and assignments are quick means to filter, hence their popularity.

* Not much of an incentive to keep applicants posted at every step, plus, managing communication with a few hundred applicants for multiple positions is hard - so you're most likely to receive only automated communication from the hiring team.

I believe that having a clear specification of the job, that can be checked/validated with applicants is critical to ensuring a smooth, fast interviewing process.

[1] - Shameless plug to my startup (in beta) - https://www.interviewpass.co. If any of you are interested in using InterviewPass in your hiring, drop me an email at suresh@interviewpass.co - happy to help set it up for you.