Only because we are left with no other options.

[If Elias could open a rift through space-time and return home (with a pit-stop in Oska to pick up Chise), he would.]

I agree with you, however. If we are to be used in this way, we might as well have full understanding of what it is we are to do and why. Keeping us in the dark will only further endanger the missions we are assigned.