Leaving aside the fact that the Economics prize isn't actually a Nobel Prize, topics which historically haven't been given enough attention are exactly where the highest impact research takes place.
If externalities had always received the attention they deserved, Coase would have never received his prize, because his work would not have been so important.
I think its safe to say that externalities are not, and were not, an ignored sector given more than a century of serious work, and the fact that it is covered in any intro level Econ course.
Inside of economics, they have more than 130 years of work, and are taught in any intro class.
If your argument is that we are bad at correcting for them, then yes. But that is different than not considering them.
Climate change has been discussed for well over a half century, yet one of the main priorities of the current administration has been to hamstring renewable energy and promote coal and oil. I think it's pretty fair to say the issue is being ignored.