Just Stop Oil targets culturally significant objects to highlight that the viewer's outrage at direct attacks on those objects is greater than the viewer's outrage at the same attacks against those objects by the creators of climate change.
If throwing washable paint on Stonehenge pisses you off, you should be even more angry at big oil for progressively destroying the entire planet. Any call for the arrest and immediate punishment of Just Stop Oil members should also match calls for the immediate punishment of big oil execs.