You may not realize that research is very unstructured and you have to find your own way. After the MS portion there isn’t much coursework and you have to come up with research and a dissertation. you have to be highly motivated and self directed. Many people give it up and even go a bit crazy and start to wonder what they are doing here. I have seen posts to that extend elsewhere. Read The PhD Grind, he did finish but it gives a good idea of one person’s journey:
http://pgbovine.net/PhD-memoir.htm