Didn't Robin strike a pose with the Straw Hats earlier this act? And she talked with Marco out in the open. She hasn't been hiding. CP-0 has info on the status on all of Kaido's executives and has the stats on the forces on both sides of the war, why wouldn't they know where Robin is? They were highlighted as not interested in taking action currently.
In regards to the Beast Pirates, Robin was looking for ways to help, Marco even tells her and Brook that they're too valuable to spend time fighting randos. So it's clear she would fight someone significant. The only issues was the trap and Robin can instantly teleport, Sanji knows she'll be fine hence he asked her. Even if someone else came after her, she can teleport away.
Let's talk as if we're the strawhats
Premise A
"Robin was already in the frontline and nobody is capturing her, Therefore Robin can travel freely anywhere she want because they (BP) seem to have no interest in Robin"
Now, i ask you, what's the difference with this premise
Premise B
"There are a group of people enjoying their time in a rainforest, they then came across a pack of wolf. However, the wolves seemed to have no interest in that group of people. Consequently, that group of people proceeded to act whatever they want since they have the premise that the wolves are not attacking them"
If you were in that group, do you think it's fine to do such act?