And at that point in time, there was really no reason for Johnson or anyone else involved in the production of Star Trek IV
(TNG was still in utero
) to think that the Transwarp experiment of ST III would be completely jettisoned between the release of The Voyage Home
and The Final Frontier
by the TNG writing staff.
When Johnson was granted access to the ST IV soundstages (the Enterprise
-A bridge sets had not yet been struck), he stuck as closely as he possibly could to what had already been established onscreen, and to the Okudagram graphics on the bridge consoles, which was the only proper thing to do, given what he was attempting to produce.
What's surprising is that the book has aged so well in the decades since its publication, even considering the continuity and dating-changes later official sources brought to the franchise.