They have done zero to destroy the durability. In fact, it’s probably more durable.
If the physical copies are scarce, that is due to the publisher and copyright laws and not them buying and converting a single copy.
Agree. While it certainly isn't the most environmentally friendly to render huge stacks of paper into waste, the real issue is copyright creating scarcity (inability to copy the thing).
Are they? Or are they just using it for training and not keeping the digital copy afterwards? And even if they are keeping a digital copy, does that actually matter if they never release it?
As for long term benefits, it could one day be sold as a service, once copyrights have expired on the works. We can't see it today, but that is purely the result of the law and what the law intended to do from the start, you don't see a copy unless you pay for your own.
You’re making a distinction here, but training is something you repeat for every new point release, so you need to keep the data if you want to use it for training.