Totally see your logic here. It's the best clue they had, why not ask the public for help?
However I also see the logic of the other side. The side that says don't release that info.
For starters, I don't think they had a good image of it. The purpose of a dash cam is more for taping officers interactions with citizens, not for identifying vehicles. It won't capture a good image of a darker vehicle on the side of the road at night as an officer passed going 60+ mph. I think all they had was: reddish, might be a Taurus, probably 10-20 years old. Not much.
The obvious follow-up: Why release info on other cars, but not the Taurus? Only FBI/DCI/Fitzgerald know the answer. Can think of two reasons: 1) those cars weren't related and they were just doing it to keep interest on the case, or 2) those cars were on video in the area and LE was looking for them to see if they could get a better description of the Taurus and/or its occupants.
I also believe one could argue that since the Taurus is the only thing they really had, releasing it means they are basically showing all their cards. If the perp knows LE is looking for a Taurus the first thing he would do is get rid of it. So by releasing that info, they are giving the perp an opportunity to remove his connection to the only thing they have.
Also, withholding it would give them something to weed out potential suspects. Call about a suspicious person comes in to the tip line. "Does he own or have access to a red Taurus? He does? Let's check this one out with a fine-toothed comb."
And finally, as I've seen mentioned before, knowing that LE is looking for a Taurus could make the perp panic. Which wouldn't be good for Jayme.
I'd be curious to know if LE was considering releasing the description of the Taurus at the news conference they scheduled right before she was found.
Again, I see plenty of reasons both ways.