What could reason could there be not to steamroll them if he wished for it?
(I’m not saying this makes it right, but there’s a long precedent for it happening)
Trying to control what happens after we're dead is normal and I guess it can fuel motivation to work harder and have a purpose, but it's kinda pointless.
In some cases there are good reasons for that, which is why common law has the "rule against perpetuities"
After all, if some eccentric landowner in the 1800s was scared of electricity and put a clause in their will that electricity could never be used on their property - why should the rightful owners of the property in modern times be bound by the wishes of the long dead?
Of course in the specific case of an author's hard drive, I think it's right to respect their wishes - I wouldn't want the contents of my hard drive published after my death, no matter how much joy it might bring to voyeurs.
In the end its up to the creator and the executor of their will to decide how their remaining artefacts are to be treated.
And with Terry I have to admit that the last works I have read were not as good as works sometime before them. So these might have been even less representative of his work.
In December 2007, Pratchett announced that he had been diagnosed with early-onset Alzheimer's disease.
He was very likely all too aware that his unfinished works needed a strong overhaul from an editor in close partnership to tease out portions that were utterly at odds with what he had intended to say or thought he had written.
In the event of death apply steamroller seems like a wise choice.
In his last years I believe Pterry was not actually physically writing himself, but working through an amanuensis. I can easily imagine that this massively complicated the revision process and the novels, probably from Unseen Academicals onwards read to me more like earlier drafts than finished productions.
Now you mention it, something did feel off with it.
I only really got pushed out of my suspension of disbelief with Raising Steam, specifically that the words "molybdenum disulphide" absolutely do not belong in any Discworld story.
It's not clear that they even mentioned to Gaiman what they were doing, and I suspect Gaiman wouldn't have wanted to disrespect Pratchett's wishes anyway.
But I think the spirit of my question was clear and you are nitpicking. So no, you did not have to point out the obvious :P
Such a right doesn't exist.