Actually the SDK for GoldSRC from Valve was the turning point back when HL1 was contemporary, followed by QERadient.
It was a Mod scene but it was extremely over saturated although very few of those projects ever saw completion many of those that did ended up becoming fairly major franchises like Counter Strike and Day of Defeat.
People have had inexpensive and free tools to create a complete games for ages and now it is just much easier to achieve a lot more in less time with fewer people but most indie projects will never be finished and of those that are very few of them will be any good.
Saying that i think we will see many more indie games come out but we probably won’t see much more competition then we have in the past.