Having been on both sides over complicated or over involved interviews put people off, fear of micro management for one.

Much better to do enough in the interview to weed out the completely useless for the role and then either do a round 2 with whoever is left or offer a 3 month probation to as many as you can and see who works.

Worst case you have paid someone for up to 3 months and not got what you need but some times people surprise you.

Because interviews are practically useless.

Harvard research demonstrated interviews are as effective as simply pulling names from a hat.

Because workers enjoy torturing people.