In his brand new commentary, Gene Green has an interesting angle on Jude’s allusion to OT pseudepigrapha:
“In each case, the incident recorded is tied intimately with some set canonical text. The angelic fall (v6) became a very common interpretation of Gen 6:1-4, and the dispute over the body of Moses (v9) was an interpretive tradition that developed due to the rather obscure reference to Moses’s death in Deut 34:5-6, which concludes ‘but no one knows his burial place to this day’ (NRSV). Jude’s reference is to the Assumption (Testament) of Moses, but it also evokes the words of Zech 3:1-2. The quotation of 1 En. 1:9 in vv14-15 draws on Deut 33:2, which was considered prophetic of the day of the Lord: ‘The Lord came from Sinai…with him were myriads of holy ones; at his right, a host of his own” (NRSV). Jude makes judicious and limited use of references to apocryphal literature and evokes only sources that tie into the canonical text and interpretive traditions surrounding it. Jude’s use of apocryphal texts is closer to canonical bedrock than is sometimes acknowledged,” G. Green, Jude & 2 Peter (Baker 2008), 32.