Five years is the standard minimum for a Ph.D. for a full-time student. Many students are forced to work other jobs, especially adjuncting but also substitute teaching, temping, and now cryptocurrency investing to make a living, and that extends their dissertation period, sometimes interminably. Often they're supporting a family. Even though they now place limits on time to dissertation, many get around through medical leave or they just work on the dissertation while out of the program and then get back in just for the defense, when the dissertation is ready. If the major professor doesn't agree to a defense date (and they do not want to put up anyone for the defense who is likely not to pass), then they cannot complete the Ph.D. So, grad students in rare cases may feel resentful toward their prof. At the same time, you can't put someone up for failure, and so they should understand. But I have seen numerous defending after ten years and some in/out of the program for considerably longer.