Idea Competitive Maps

It's simple, small, and has a relatively low amount of jank—bars pass being the notable exception. That set of qualities makes it very easy to refine gameplay on that map in particular. The same goes for Airlock I. There are aspects of these maps that have been tested and countered over and over again, like spots for archer and assassin, as well as what classes are better on those maps.
For a lot of active members of the community, playing on Blackout or Airlock I is like second nature, partly because of the frequency of play. and partly because of how easy it is to refine the gameplay on those maps.

Whether or not Blackout is the "best" map is up for debate (and a lot of it, too), but it's often the easiest one to play because of how accepted it is within the community. Blackout is by no means balanced—archer, ninja, soldier, and assassin carry a lot more weight on Blackout than a lot of other maps. But asymmetrical design doesn't make the map bad, it just means that it allows for a bit of extra strategy. In fact, the polarization of the classes is another reason the map is so refined; if you don't need to worry about half of the classes, your job is that much easier when practicing!

Sorry for the long response. Hope this answers your question.

 

Simple design, good size, playable for all classes and focuses on gameplay over looks.
4 concepts that new maps are lacking greatly.

 

its like dust2
people only like it because they dont know any better