I actually find it weird that you got no reason. From old days, I remember they used to specify the reason.
I see a few complaints here and there that Google started disabling low-traffic sites. Maybe they are trying to increase the quality for advertisers.
Not sure if that's your case but of it is, you should be good to go when the traffic increases... But that's just an assumption.. I haven't done AdSense for years, so all I have is rumor :)