Digimon Savers / Digimon Data Squad

[The Reclaimer]

The Royal Knights were doing what Yggdrasil wanted them to, like Unknown said.  He was trusting in Daimon Suguru's word that the Digimon slaughter (in which Ikuto's "mom" died; which was a suprise attack).  Digimon did not attempt to open Digital gates because they seemingly don't have the technology to open and close them.  Now they could have used Mercurimon's gate I'm sure, but then there is questions that would result from it:  Where would he land? (If you recall DATS escape they landed in a river, certainly Ikuto would have drowned)  If a Digimon took him back, how would they return?

These would have been unnecessary had Yushima and Satsuma been working with the Digital World directly but they were just doing their directive duties for DATS as instructed

Why would they help with Belphemon, he was doing no harm to the Digital World and by the time he caused the time-space problem he was destroyed.

So to sum that all up, and agree with Unknown: They did exactly what their God told them to do.