why did the alpha trolls' session fail?

They weren’t coordinated. There was too much internal trouble, Damara /snapped/ coerced by Meenah to the brink and then led to the dark side by Kurloz, there was death and in-fighting and no one wanted to actually get shit done. But ultimately, while their Session overall was a complete mess?

Their Session failed because it was Glitched.

They were the originals. The first ones, they were like the Beta Kids’ group to the Alpha Kids. But their Session had a big Glitch. Little is known about the Glitch other than it seems to be actually influenced by Lord English, a calling card of sorts. And when this Glitch happens, shit gets weird. In the Session, they had everything they needed to win, arguably. They’re never said to have been in an unwinnable Session, it’d seem that they all had the required tools and Players to complete the game if they had just been less of a group of fuck-ups. But even if they did win? They would’ve been in a Doomed Timeline.

Because they would’ve never been born.

The Glitch is simple. There’s no Ectobiology in the Session. Whatever there is in the labs at the Veil, it’s not the Ectobiology devices to make babies. Just your standard Carapace Ectobiology, arguably. The Alphas never made themselves. They were meteor babies, but they never had Ectobiology to create themselves. And so, Paradox Space required a Session where they would be born. And since it wasn’t theirs… It had to be from a Scratched Session that wasn’t Glitched.

It pretty much forced the Scratch to happen in the Blue Universe, because it needed to retroactively happen for the 12 Alpha Trolls to even exist in the first place.