The main reasons that employers move towards hiring interim contractors are:
Speed
You’ve got a crisis situation. You may have a vacancy where a key member of staff has moved on and you’ve since struggled to recruit for the permanent position.
In this case, you can usually engage an interim who is able to start immediately or within a week or two, provided they are not already signed up to another engagement.
Skills
It may be that you want to upskill a team. You’ve got a skills gap and you need to get someone in straight away that has the right domain experience that your team requires.
At the same time as delivering a project, the interim contractor can upskill the wider permanent workforce by training and simple cross pollination.
Project work
Your business needs to deliver a project that you don’t currently have capacity for internally. But you may not have the budget for a permanent hire or you may only forecast needing these skills for a short period of time.
Interim recruitment is specifically helpful when you are a business that is testing something, building something new, or investigating new markets or product lines.
Risk
It could be that the business is not ready to fully commit to a project by building a team or investing in permanent hiring. So investing in interim recruitment and interim support is less risky.