While I do understand to wait for people to receive a pdf before releasing the pdf to the wider public...I dont understand this approach of waiting for physical books to arrive before releasing a pdf.
You mean retail release?
I don't think it makes sense for them to separate the pdf and book version release for retail. So if they wait for the ks distribution of the books to be roughly finished, they almost have to do so for the pdf version.
If they
have to wait at all is more a philosophical question (and a matter of what they may have promised - not sure what the stance was on that), that goes far beyond this specific release.
Myself, I never found it that interesting when other people would get stuff (earlier/later) as it has not impact on my enjoyment of a product. Besides given ks wonky timelines, backing because you expect something early or in a specific time order was always a very optimistic approach.
Particularly ridiculous were projects where you pay different prices for different delivery/production waves, because with shifting timelines the distances between those waves (and whatever you as a backer assigned as good price for that distance) almost never work out.
But I am digressing. ...