Well, my guess is, that it was so easy to get, because it wasn't popular. It's the two plane mechanic, which also made RayCrisis an overlooked game. RayStorm's popularity is also owed more to its groundbreaking 2.5D visuals, than its gameplay. My answer is just a theory, but..
I'm currently playing Xevious 3D, another two-plane shooter, and though it's a great title with a lot of dense sci-fi atmosphere, it's also very hard to get into. It's not only the two plane gameplay, which makes it so hard, but also the shot trajectories: from three shots of an enemy, only one is aimed at your ship, while the other two will cover the area next to it. The result is, that you can't make bullets follow you properly and get shot by seemingly aimless projectiles. This, coupled with the slow speed of your ship and the fast growing rank, makes it unnecessary difficult to dodge, ultimately killing a lot of fun to play this game.
I could imagine that those flaws mentioned above not only made Layer Section unpopular, but also all the other Xevious-like shooters. Think of Terra Diver, such a great title, but not really played that much and still widely available, too. It's probably because those games require a different approach, like a constant rank control and a different dodging strategy. A lot of thinking's involved, real-time, and that just kills the casual aspect this genre's famous for. A bit like a Treasure game, yet one w/o any innovative gimmick to make it up to you. Too bad.