Yeah, there is a reason. Because they're afraid everyone will flip out again. Maybe 3 of the trap would still be too much depending on what else they let up on for the deck. But I guarantee you that 2 onslaught won't destroy the whole meta. Subterror has all 3 of their fifty billion effect trap card and they aren't flying high, so onslaught is hardly OP anymore. But the skill may be too much.
Eventually, I think it was the swordswoman who became a bigger issue to deal with in amazoness than onslaught. If they ever put princess back to 3 and onslaught at either 2 or 3, the swordswoman could go to 1.
And she will get village in her starting hand what feels like every turn. I haven't had a chance to get to the GX Cup yet today, but they made Zane use cyberdarks and not cyber dragons? I guess after this tag duel Aster might be the partner.
For me it was mostly this:
DM Cup- Zane with cyber dragon deck and Mai
5Ds Cup- Alexis with aromage deck and Akiza
GX Cup- Aster with masked hero combination deck and Alexis
Special Cup- repeat DM and GX teams