Thoroughness of the interview process typically relates to the amount of skills required for the job. Engineering requires a tremendous amount of skills, and so

Thoroughness of the interview process typically relates to the amount of skills required for the job. Engineering requires a tremendous amount of skills, and so it requires a fairly thorough review process. Being a cashier, for example, requires very little training. You could hire somebody after a 15min interview, and if they turn out to suck, fire them and move on with very little lost. That's not the case with an engineer.