It is true that friends share information. It is also true that generously sharing information with someone may be one of the steps that leads towards your becoming friends. But this isn't transactional. You don't "win" a friendship after sharing a certain number of pieces of information.
What's more, the fact that these people do not thank you, and do not do it back, may be a clue that they don't see your information as a generous gift. They may interpret it as you showing off, butting in, telling them what to do (what class to take, where to eat, where to study) when they didn't express any interest in suggestions, and other activities that work against friendship.
From a interpersonal skills point of view, questions are your friend here. If people are talking about where to go for pizza, and you offer suggestions on where to go for Thai food, or a quiet place to study, you're shifting the topic and some won't take it well. Asking "is it pizza for sure or would a nice Thai place be interesting?" is less of a jar. Or "is everyone going for pizza, or is anyone interested in still studying, maybe somewhere quieter?" Similarly, if a particular activity (like applying for fellowships) is underway and you wish you had information, you can ask people "where do you find out about good fellowships?" Keep in mind, though, that if I tell you about a fellowship I applied for, I might be lowering my chances of getting it: this information is very different from how to get a housing subsidy or what classes another department offers.
In terms of your own feelings about how your suggestions are rejected or don't earn you anything, may I suggest you have a long think about why you give suggestions. Is it to look smart and well connected, so others will admire you? Is it transactional, so that they will give back what you gave? Is it generosity and wanting to share with others without expectation of return? In your own heart, come terms with your reasons and then live by those reasons. If you are giving for no reward, stop counting the rewards you do and don't get. If you are showing off to feel smart, enjoy that feeling when you experience it and don't look to the future for a return on it. If you expect a return, make that clear. "I know a super cool study place, I don't tell everyone about it, but if you can let me know where you got that cool pen, I'll tell you my study place." Done right, that can actually be fun.
Not everyone you go to university with will be your friend, even during your studies never mind for the years afterwards. I still have friends I met in 1977. I can assure you we have given and received a LOT of information over the decades; but that is not what made us friends or kept us friends. And of course there are hundreds of people whose names I once knew who were in some of my classes and who might have told me interesting things once or twice but never became my friend. That's ok. That's how university is.
