Most hiring managers are hiring people because they have a definite need for a developer. Every day that they don't find one, they have work that's going undone, projects that are proceeding too slowly, bugs going unfixed. And if they're not finding people, after a while their directors start to question whether they're doing their job properly.

There is nothing a hiring manager loves more than finding a hire-able candidate.

That doesn't mean that the interview is going to be a cakewalk, though. The hiring manager wants someone who's going to be a success in the job, and they're going to try to filter for that. The only thing worse than not hiring a good developer is hiring a bad one, and the process is trying to stop that latter from happening, too.