There’s a bit of a difference between a ship already at sea altering it’s course to get near and assist a vessel in distress (where they might be first on he scene), vs ship going to sea especially for an event I guess? You don’t want the area too crowded with “good Samaritans” who’ve all gone to sea just to assist.

I recall some comments saying that operators of a submersible that could hypothetically rescue a sub stranded on the bottom being discouraged from deploying for the Titan by the coast guard, which perhaps means they already knew the fate of the vessel. Although it could be that they already had a suitable submersible arranged already and didn’t want more in the area causing complications with coordination etc.