Probably researchers working with grant money, or people in corporate R&D with tight deadlines, but not so tight budgets.
They also save you from having to learn how to actually design the board yourself, so if you don't know how to do that with modern tooling, then you can pay $1000 for someone else to do it per board, rather than hire someone out of your project budget to do it.
They also save you from having to learn how to actually design the board yourself, so if you don't know how to do that with modern tooling, then you can pay $1000 for someone else to do it per board, rather than hire someone out of your project budget to do it.