Venom geek media did a really good video on this subject. His theory was that the change to a vertical warp core over the prior horizontal core resulted in too many compromises. Most notably the way the new vertical core overlapped with the photon torpedo launchers could cause the catastrophic loss of the ship in the event of an unlucky shot.

https://youtu.be/aSmNFONa7Lo?si=tPDTtvIQ2gte7Zjr