I don't think going over the hours is problem at all.
I don't think it is fair to say "I can't understand why people go over.."
well, different people hit snags with different aspects of the course. There was a chap at my school who had terrible problems with navigation and had to repeat a lesson a few times. He eventually ironed out the problem and passed the test. Some people struggle with the instrument part as well.
At the end of the day, the reason people go over the prescribed minimum is simply down to the fact that they are human and we can all make mistakes!
I hate people stating that the CPL is a glorified PPL, because it simply isn't and my experience, and the experience of the other students on my CPL course would back that up.
I had a decent standard of flying going into the course, but my flying was completely dismantled and put back together again, but in a different way- if you get what I mean.
The CPL course is hard work and does demand that you change your thinking towards flying-captaincy skills, workload, precision etc...
I heard it mentioned in the school that people do approach the CPL course thinking that they do not have to put any work or study into the course, because there is this idea that it is a "glorified PPL" or simply because they have done the ATPLs and this is a piece of p155.
It was hard hard work mentally and physically and you do need to approach the course with the right frame of mind and don't think of the course as a jumped up PPL. Attack the course with the same enthusiasm/hard work as any other course on the build up to your Frozen ATPL.