In ye olde days back in the 60s and 70s there were no man made base oils or high tech additives. The only way to give protection in highly stressed engines was to use thick base weight oils ( straight 40 or 50 ) .
Where a separate gearbox existed they could use extreme pressure additives to combat wear but these additives could not be used in the rest of the engine.
Ducati bevel systems recreate the severe chopping action as in the gearbox so give their oil a really hard job to do. In the 70s straight grades or castor oil were the only options. These oils needed very careful warming up , especially on cold days, as they are very heavy when cold anyway . There was always cold wear issues if you start and ride off straight away.
TRM is a modern solution to these types of older engine requirements. It has a clever balance of the biggest molecule man made synthetic base oil along with traditional bright stock base which is the biggest and best type of normal mineral oil. The additives give the best anti-wear and extreme heat protection available. It has fantastic cold flow for an oil with such heavy base as there is virtually no wax content from the bright stock. This gives far superior start fluidity and initial protection throughout the engine. These bases just do not break down with the heat as traditional mineral bases of equivalent viscosity would do. The bevel and gear protection is second to none. Engine component life is greatly extended when using this oil technology. It was not available when these engines were designed and built.
So there you have it, a brief explanation as to why we use more modern oils in classic motorcycles.