From being on various recruiting positions, I believe it's usually just incompetence or laziness.

Hiring tends to happen when there's not enough people. Only the people who can do the job are qualified to assess whether someone can do the job. So you have people who are already at double the workload having to take time to design and handle interviews and such.

And by the time you get everyone to sign off on hiring this guy at the extravagant tech salary, economic downturn forces you to fire a bunch of people. In a recession, the least useful people are probably HR.