It sounds like you were brought up well and now have wonderful personal traits. Unfortunately, not everyone is like you. Sometimes it isn't even a matter of upbringing because I have witnessed this within my own family, to my surprise.
It is pretty uncommon for people to send thank you notes lately. They don't even send out invitations, it is the new thing. They text or FB. While some of us are offended, some are perfectly okay with it.
As well, people talk less and less with online communication taking over. While working the other day, I called a young man and his voice message said some pretty rude things followed by, why are you even calling leave a text message. Really, that is what it has come to. My nieces don't ever answer my calls, but they will answer a text message. And they never call me or text me. From what I hear they don't call or text their mother either. On the other hand, my daughter and I communicate with a text or phone call daily. I also have some clients, usually the younger generation who do all of our business communications on text. The verbal communication is nearly out the window.
To share some of my personal let downs...my cousin. She plays a lot of games and sometimes you are not sure you are the victim of her BS, but you think so. Well, she finally did a few things that rubbed me the wrong way and I just stopped talking to her, because if you confront her, she will deny it. So now she sends me group text messages. You know this because everyone's comments show up on your phone, even the people you don't know. So I don't responded. Now she is asking my husband, rather than call me, why I won't answer her texts. It disturbs me why she cannot send a personal message to me and why she would think I should respond to her mass message. I send her daughter my daughters clothes and I don't receive any type of acknowledgement. I do this at church and I see her on Sundays...when I see her on Sundays, I usually don't get any more than a hello, if that. Why can't she talk????
Here's another. After my mother had surgery to remove her cancer I called my childhood friend. I wanted to let her know my mother was okay, as we had already called her mother when my mom was out of surgery. She spent the entire phone time talking about herself and then said she had to hang up to get ready for dinner with her best best friend. I never got to tell her my mother was okay. This was 3 years ago now mid January...she never called back.
So I totally understand it is upsetting, but don't let it bother you too much. Many people are like that now. Maybe there are issues we don't understand, such as the possibility of depression.
Keep doing what you do because you sound like a very good person. Don't allow this to change you.
Also, someone on here once wrote that an average friendship lasts 7 years. Perhaps both your college friendship and my cousin and childhood friend are just over. I guess we both just have to move on and find new friends.