If it helps, I moved out of a city I lived in... 7 years? Not a single goodbye. Not even from my closer friends, people who came to my wedding (years later) who were busy with their own shit when I moved. We kept in touch over text and whatnot after that. We were in an improv troupe together, we did my last show, I moved out a week later and that was that.

Try not to get your feelings hurt (lol I know that's impossible) but remember this isn't truly reflective of your relationship. People will say goodbye if you have a big party or you pull them aside to let them know. Otherwise it just doesn't register. They busy. They have their own big worries. It's not that you're not important to them, it's that they have their own stresses.