[fidelis]

Assume that the account in Maccabees is true. Suppose then that one had authority in that unsettled era and wanted to assure that the Ark would not be found and taken or even despoiled.
Would you leave the Ark on Mt. Nebo and trust to its security even though that was its declared resting place? Or would you secretly move the Ark to somewhere new, letting the account in Maccabees stand as a way to divert attention.
Call this speculation, but it does offer an explanation for why the Ark has not been found.

Assuming the account from 2 Maccabees is true, part of Jeremiah's instruction implies that no one will know or find the location until certain pre-conditions are met: "The place shall be unknown until God gathers his people together again and shows his mercy. 8And then the Lord will disclose these things, and the glory of the Lord and the cloud will appear, as they were shown in the case of Moses, and as Solomon asked that the place should be specially consecrated." None of these conditions, as far as I know, has occurred historically. Maybe one could speculate that it's possible that somebody stumbled across it and hid it, but the appearance of the glory cloud as it was in the day of Moses and Solomon, for example, would be impossible to hide.

[Rockingham]

I am unwilling to credit Biblical prophecy as true in every jot and tittle conveyed by modern translation. Moreover, a close reading of Maccabees might distinguish known as meaning known to the people, not the secret knowledge of those who may have moved the Ark from Mt. Nebo to a new location to protect it.