Very few people use the Flash IDE for serious development. Code is contained per animation frame which is absolute hell for anything more complicated than a single button banner ad, and Flash IDE files are completely unmergable via source control tools. The only people using the Flash IDE are banner ad developers and cartoon developers (of which there are surprisingly many -- even broadcast animations are often done in Flash these days, and then exported to Quicktime for delivery).
If you're making games or apps for Flash, you're using the command-line compiler (either directly, or more typically, indirectly via Flex Builder). Further, if you're doing anything that requires good performance, you're using the (not very good) bitmap support, and completely avoiding the vector drawing model, as it's so slow to be unusable in most interactive contexts.
Flash exists because Flash exists, and for no other reason. It's not a particularly compelling environment compared to, say, Unity3D or some of the other recent browser-and-desktop plugins. Hell, even Java is generally more pleasant to work in. The sole advantage to Flash is that everybody already has Flash installed.