BOOM
I think there are two different justifications involved, and each justification feeds a different argument or theory.
Some are of a mind that the Page/Strzok love affair is pure fiction, and as the sole point of evidence, they cite a total absence of lovey messages. That observation is also explained if the DOJ withheld all the purely personal messages.
Of the messages that are not withheld, there are likely portions redacted at least from the public. I would take those as protecting either classified information or ongoing investigations.
On reading that, I wonder if you are thinking of the 50,000 that were missing. Cough cough.