DDoS attacks used to be only a temporary issue where if one bought the site down you'd simply wait it out and after a few days at the most you'd be back online with everything back to normal. Over the last few years however we have seen much more relentless attacks that never end unless the attack is beaten and then the DDoSer will usually do one of a number of things: they will either give up, give up for now and come back with either a different type of attack or a stronger one, or they will up the attack even more there and then. Obviously if they keep upping the attack and the mitigation keeps the site online they will eventually give up for the time being at least. What's happened is sites have been attacked without sufficient DDoS protection and they've waited it out like the old days only to be shocked that it never ever ends, if the site is null routed the attack may then stop temporarily, but before long the attack will re initiate again after returning online, as many sites find out the hard way this can happen even if they're offline for ages, although it could take the DDoS a day or two to notice, that's all. We have also seen types of attack against the site or tracker itself that bypass the hosts DDoS protection, thankfully in this situation there are things the system administrator / sysop can do up to a certain level in this situation (I'm not going to go into full details here).

As far a gaming trackers, well a lot of different types of trackers have been affected in recent years, not just gaming and a lot of attacks actually get mitigated without members even realising as it's probably not a good idea to give a DDoSer recognition unless you have to, E.g. when services are affected, as they want attention. I think gaming has come more to everyone's attention at the moment because an attack bought down GGn recently for an extended period.