It's important to realize that other people may have something going on in their life that affects their mood and maybe their desire to be friends. If it is someone you know at work they may not be comfortable talking to you about the problem. I think you should always be friendly, but if someone isn't friendly back don't just assume its because of you.
1: Befriend one of the front-end developers 3: The dev stops talking to me, becomes a lot less happy overall 4: The dev quits
In my case, what I didn't know about for a while was 2: The guy got put on a PIP for dubious reasons and got absolutely demoralized.