There are some people who look at the shortage of priests and suppose that a Diocese would be eager to accept candidates without a lot of consideration. This is not true.
The Vocation Director of the Diocese will interview a candidate carefully to determine if he feels the candidate has a legitimate vocation. The motives of the candidate will be explored in depth. A priest who applies to a Diocese to which he has little or no personal connection will raise flags, but is not a cause for categorical denial.
In many Dioceses, the candidate is expected to already hold a four-year college degree, but the Diocese will pay part/most/all of his seminary training (which confers Masters Degrees). This can be a considerable investment for the Diocese (often six years of instruction). And it’s not unusual for candidates to drop out before Ordination.
In past years, candidates signed contracts to reimburse some portion of the cost should he drop out. This was a bad idea - it encouraged men to conceal their lost sense of vocation and continue onto a ministry that they were unfit for.
So the Diocese takes all of the risk if a candidate drops out. It is financially incumbent on the Diocese to select only men whose vocations appear legitimate, so this is one reason that their motives will be carefully scrutinized.