Teams become good by competing in real, difficult competitions on a regular basis. The 'regular' and 'difficult' parts are important.

Up until Bliz announced HGC, there was absolutely no financial incentive to play hots competitively in NA. Even if you were really good at the game, unless you could guarantee top 1 or 2 finishes, you're making no money, and you have minimal or no organizational support at all. This situation has only continued to deteriorate since C9 and Tempo Storm left NA hots because there was no money in it for the orgs. Sponsors weren't interested in hots teams, apparently.

Hopefully HGC will reverse the trend, it at least guarantees compensation that you could hypothetically live on for the top 8 in NA, and should produce more stable teams that can regularly compete with eachother. It is important that the teams outside of the top 1 or 2 be actually good enough to offer significant competition, because that's what improves the overall level of competition, and it's also important that they play regularly in actual tournaments. Scrims aren't enough.