There was no such delay. The bulk of the manuscripts have been published as they have been restored and they have been published into modern language translations almost as swiftly.
The “50 year” bit is in regards to scholastic turf wars.
The initial group who got possession of them was a multi-ethnic/multi-national/multi-faith group of scholars who happened to have a preponderance of Catholics among them. (As the largest single group providing scholarship, that is not, in and of itself, surprising.)
At some point, all of the collected manuscripts were photographed as a backup and the photos were sent to Stanford University for safe keeping. Meanwhile, the originals remained in Israel under the protection of the original group (with a slowly changing membership due to age, retirement, etc.).
Once all the “big” scrolls were translated, the next job was to take the enormous number of fragments and attempt to piece together larger and more coherent scrolls from those fragments. Here, the turf wars began. The society that had possession deemed themselves the only legitimate group sufficiently well versed to handle the reconstructions. Other scholars who asked to review the reconstructions were turned away. Nasty comments were made by each group regarding the other.
At some point, (early 1990s?), someone at Stanford decided that the next best thing to prying open the door to the study society in Israel would be to publish the photographs of the fragments. This was met by loud cheers from the people who had been denied access and much tongue clucking from the study group who issued condemnations of the breach of “trust” along with (some accurate and some wild) claims that studying the photos was inappropriate since the photos could not present the true appearance of the fragments.
Once the photos were published, of course, people could also look at photos of earlier scrolls for which the transcriptions and translations had been challenged. Much was made of that, but I am unaware of any serious challenges to the original scholarship. (They were not incompetent conspirators, just scholars jealous of their turf.)
The fragments are often tiny with a sentence or a word or a letter as the only remaining portion. A few have been pieced together to create mildly interesting (suggested) larger fragments, but there have been no new “books” created from the fragments.
As noted, the study group and its administration were top-heavy with Catholics. This has really fed the fires (outside the realm of scholars) among conspiracy theorists, despite the fact that the RCC has no direct control over the original scrolls and no “Catholic” transcriptions or translations have emerged from the group.