The power consumption of turbine oil pumps is pretty low. My best guess would be less than 10hp for these engines. That leads to comparatively 'low quality' driveshaft arrangements. Remember that a number of cars use plastic water and oil pump drive assemblies due to those low power requirements.
Shrink fit shaft arrangments tend not to be preferred because their strength is highly dependent upon fabrication tolerances - hence the use of splines in the majority of high power applications.
In theory reasonable quality control should mean these sort of shafts are 'fit and forget'. But if it can do wrong, sooner or later I suppose it will and that seems to be what happened here.
The saving grace in this case was the 30 min emergency system and good decision making by the crew.