HR will be running the process and posting roles, doing the initial sort of applications and being the first point of contact for candidates. The department head will want to be kept informed and perhaps have a say in the decision making.
There could be other folks involved in approving offers and signing off on salaries, too.
Recruitment isn’t any of these people’s day jobs, and they’ll be trying to fit this activity in around other priorities, which is one source of delays.
At each step of the selection process – initial sort, first interview, second interview, possibly a task or a ‘meet the team’ opportunity – two or more of these people need to get their diaries aligned to run the activity and then agree on which candidates go forward.
They could be doing this for a dozen candidates at any one time. And there’s a lag from posting a role, to getting applications, to arranging interviews for everyone, to arranging the next round of interviews, to getting the offer approved by higher ups, to waiting for the first choice candidate to respond…etc…
All of which takes time. In a fast-moving agile organisation that prioritises recruitment, it might be done within a week or two. For a more bureaucratic one, it can take months.
This creates a lot of frustration for candidates, particularly around time-frames and communication of next steps. And you should plan to be involved in several processes before you’re successful – there’s a lot of competition out there.
So, to answer your question directly – taking a temporary job is a question of money. If you have bills to pay, don’t rely on the job search and application process being quick!