The banks will NEVER give you specific reasons. They don't have to. Giving you details only opens them up to being sued. Why should they? The simple bottom line is that you did something (probably lots of things) that they didn't like, and at some point they just decided enough was enough, and they just weren't that into you.

Surely you can think of some things you did that pissed them off, no? You may not know the exact thing that pushed you over their line, but I'd guess that you can imagine some things you did that they would not have liked, any of which might have been the last straw. That's the risk we all run when playing the game - you only discover where "the line" is after you've been told you just stepped over it. Up until that point, it's all "yes, sir, how can we help you?" After they decide they no longer want you as a customer, they have no reason to waste time explaining anything.

It's a bad place to be, for sure, and you have my sympathies. Hope I never find myself on the other side of their line.