I guess ALtcointsTalks is more lucky, or they still fly under the radar 
There is no inexplicable reason why random sites are being attacked. Altt may have been under the radar until now, but for example, Bitmover's site, which is smaller than Altt, was under a DDoS attack two months ago.
Those attacks are expensive. I think the best is to wait a few days... it will pass. Just like happened to talkimg.
As far as I understand, talkimg suffered seriously because of that attack, I think even the server was changed.
It's not just a matter that things will calm down with time, but everything requires more attention, and more engagement for remediation, which are always additional costs for the site owner.
Such random attacks on smaller sites as well, the only explanation for them is that they come from companies dealing with ddos protection and online security. It only benefits them.