There is a lot to be said about how difficult the job market is for candidates, but it has to be acknowledged that hiring is no walk in the park, either. It takes real time and effort to match the right person with the right role and see that pay off as they adjust to their new position. Even experienced hiring managers don't always get that right, because there is so much to consider. It's normal for everyone involved to have a slightly different idea of who the perfect candidate is.
It goes without saying that this can be very frustrating to anybody who is applying for a job. They may feel like they are perfectly suited on paper, but then those in charge of the role decide that they need something different. At its worst, a company can hire somebody who seems completely unsuited to the person who also applied for the job, although they will certainly have their reasons for that choice. The situation can be even more awkward when somebody goes for another role at their current employer and gets turned down in favor of someone else.