They pretty clearly state their metric for performance is "unicorns per $1bn" (3.08 vs 1.22).
They're suggesting dollars invested in UK startups are more likely to create a unicorn than those same dollars put into us startups, hence higher performance.
This doesn't explain though "why now?". All of these reasons would make sense, but they've been in legal disputes before in the 13 years since the game came out. And why would they suddenly care about players' frustration? The skins economy isn't wildly different now than previously.