Also why, could or would not, Jesus slander the devil? For it says he would not dare?
Literally, it says "He was not bold to bring a judgment of blasphemy." The ESV renders it "did not presume."
2Pet.2:11 (parallel text) reads: "whereas angels, though greater in might and power, do not pronounce a blasphemous judgment against them before the Lord." The point here seems to be that it is characteristic of ungodly men and false teachers that they make bolder pronouncements (in sin and ignorance) than the angels who excel them make.
Whether Peter has the Zech.3 text in mind or not, Jude makes an explicit reference to that passage. As if to say,
No, not even the chief of angels is unguarded in his speech; instead referring the urge to execrate (one who richly deserves it) unto the highest of Judges.
This is, in fact, the very manner of the Incarnate Christ as well, who said, "For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him," Jn.3:17
And Jn.12:47, "If anyone hears my words and does not keep them, I do not judge him; for I did not come to judge the world but to save the world.... For I have not spoken on my own authority, but the Father who sent me has himself given me a commandment--what to say and what to speak." Cf. Jn.8:28, "I do nothing on my own authority, but speak just as the Father taught me;" Jn.10:18, "This charge I have received from my Father;" also Jn.14:10; 7:17.
It well befits the Second Person to refer judgment (for the present) to the Father, "You judge according to the flesh; I judge no one. Yet even if I do judge, my judgment is true, for it is not I alone who judge, but I and the Father who sent me," Jn.8:15-16. He will be the agent of the Father's justice
at the appointed time, Jn.5:22. So for now, he restrains himself.
Is Christ not the Captain of the Lord's Armies, Jos.5:14-15? He is the King of kings, the Prophet of prophets, the Priest of priests. He is the Angel of the Lord; why not the Angel of angels, indeed?
Here are the key references:
Dan.10:13, "Michael, first of the chief princes"
Dan.10:21, "Michael your prince"
Dan.12:1, "Michael... the great prince who stands for the children of your people"
Jud.1:9, "Michael the archangel," (or the chief angel)
Rev.12:7, "Michael and his angels"
These are all testimonies of the highest rank. Who more proper to "stand" (as the Advocate or Defender) of his people than the Son? The OT references are shadowy, but that is only to be expected. But as Jude interprets Zech.3:1-2, there are four parties present: Joshua, Satan (the Accuser), the Angel of the Lord, and the Lord himself. In v2, it is not immediately obvious that the Angel speaks. It is said that the Lord speaks, making reference in his speech to "the Lord."
Jude infallibly interprets for us by identifying the speaker as the Angel, who is therefore also wholly identified with the Word of the Lord (so much, that it is said the Lord himself Speaks). However confusing this was to the OT people, and perhaps the prophet himself, under a NT age of revelation these mysteries are far less obscure. And it is Jude, therefore, who applies the name "Michael" to this Angel.
As an addendum, the term "archangel" is a NT word, used only twice (I didn't find it in the LXX). In 1Ths.4:16, it is said that Christ comes the second time "with a shout, the voice of the archangel." I don't think we need to find another being to utter this cry than the One who comes. Whether there was Jewish speculation about ranks of angels, and names for them, is not really significant for biblical interpretation. It may be that such an elaboration on a spiritual theme (angels) reflects pre-NT attempts to understand texts like Dan.10-12. It takes real, heavenly revelation to bring the full truth entirely to light.