Keep anon or delete as I know people on here.
I think I may know why people are "lonely at uni". I'm having gonna have a crack at explaining it. Bascially, it depends on whether you are an extrovert or introvert. Introverts will be the "lonely" ones creating these "lonely at uni" threads, however most of them will find friends later on and realise that the reason of loneliness was just natural in the first place because of the nature of the introvert.
Extroverts: If you are an extrovert you will be placed with a random group of people at uni in your halls and you talk to people to start off with. They are more or less aquaintances but if you get along with them "enough" then they become "friends". Also these guys are capable of meeting a couple of people in lectures, a couple of people in seminars and a couple at societies. However, none of these friends are what you call close to begin with, but extroverts don't expect many close friends, especially straight away. Eventually, over time, they will find people who click within their groups and then that's when close friends occur. Overall, extroverts are used to having a lot of friends, huge circles in fact, but only like to have a couple of close friends.
Introverts: If you are an introvert you will be placed with a random group of people at uni halls and will talk to people to start off with. You will only go for those who actually really click with you and won't bother investing your time in anyone else. However, introverts will find it is rare to find people you actually click with perfectly straight away, so they will end up neglecting most people and this may even include all people in the flat, hence why they are lonely and there are so many lonely threads. Also these aqaintences in uni halls remain aquaintances as introverts don't bother getting to know them, even if it is just by hanging around them/general talk; introverts will neglect them and in turn will get rejected themselves. However, introverts may still participate in societies, mingle with people on their course; what now happens here is that the introverts will find like minded people (as you would if people are doing the same course/hobbies as you do) and they will tend to make friends that way. Overall, introverts will end up having few friends, maybe even just one circle, however they will be very close friends, which is obviously nice. Introverts will generally take longer to make friends becuase they are only in search for close people who they click with very well, this will happen, but it will take time to find these sort of people, hence the "lonely at uni" threads in these forums (notice most of the threads concern 1st year students and hardly any 2nd/3rd year ones - thus it shows close friends are eventually established).
What are people's views on this? Add more to my argument if you can.
Also if it helps credit my analysis here, these are one of many social aspects I am studying in my degree module at the moment, and it is a prestigious degree too!