IIRC, the research in animal models showed that when the sheathing around the neural tube in the spine is damaged, the surrounding tissues release a kind of toxic agent that then further degenerates the tissue inside leading to localized apoptosis, and scar tissue formation at the injury site, which is then what prevents regeneration of the neural bundle.
the olfactory bulb transplant proceedure puts specialized basal and glial cells into the mix, which carve paths through the scar tissue and guide axon growth through it, allowing the axons to reconnect. In the case of the trial proceedure done in europe, where the guy is now "walking" again (with a walker), they also introduced a severed section of tendon as a graft medium, as a significant portion of the neural tube had been lost due to this apoptosis-- IIRC, a good 2 to 3 cm worth.
The process was novel, because nasal neurons were not thought capable of relaying motor stimulus signals, and thus not suitable as a reservoir of suitable transplant tissues, despite being basically the only fully and freely regenrating neural tissue found in humans. (whole new neurons are produced and integrated by the olfactory bulb. Not just old cells learning new tricks.) The trial proceedure however demonstrates that this is not the case, and that olfactory neuron precursor cells and glial helper cells can be used thereputically for motor and sensory nerve damage related conditions.
Give it a few decades. I bet people with serious spinal trauma will be treated with the regularity that open heart surgery is done now.