Thanks for your question.
The JW's teach that Jesus and Michael are the same because they are desperately looking for confirmation, no matter how tenuous, of their mistaken belief in the pre-human existence of Jesus Christ. If Michael the angel mentioned in Daniel really was Jesus, why wasn't he named Joshua [Hebrew form of "Jesus"] instead of Michael? There is no valid scriptural reason for identifying Jesus with Michael.
Here is some more information on this topic from a link called "Wrested Scriptures
" - a valuable resource for reviewing the passages brought forward to support a variety of false ideas including this one about Jesus and Michael.
The Bible mentions Michael five times: (1) "one of the chief princes" (Daniel 10:13); (2) "your prince" (Daniel 10:21); (3) "the great prince which standeth for the children of thy people" (Dan. 12:1); (4) "the archangel" that had a dispute over "the body of Moses" (Jude 9); and (5) a participant in a heavenly conflict with the dragon (Revelation 12:7). In none of these passages is Michael ever described as the Christ, nor called Jesus.
These verses are cited by J.W.'s to support the doctrine that Jesus Christ was a mere angel, who was somehow "born" as a human at a later date, died as a sacrifice for sins, and was raised up from the dead as an angel once again. They refer to him as "Jesus Christ, whom we understand from the Scriptures to be Michael the archangel..." "The Watchtower", (Feb. 15, 1979), p. 31.
The JW's doctrines regarding Jesus have changed over the years. For instance, in 1879 they denied that Christ could be Michael the Archangel! From their own Watchtower magazine, the official mouthpiece of the organization, we find these words:
Hence it is said, "Let all the angels of God worship him"; [that must include Michael, the chief angel, hence Michael is not the Son of God] and the reason is, because he has "by inheritance obtained a more excellent Name than they." (brackets theirs). "The Watchtower", (Nov. 1879), p. 4.
This is just one example of how the JWs have changed their doctrines over the years.
The book of Hebrews makes it clear that no angel has ever been called THE Son of God: "For unto which of the angels said he at any time, Thou art my Son, this day have I begotten thee? And again, I will be to him a Father, and he shall be to me a Son?" (Hebrews 1:5). The Son of God was superior to the angels: "Being made so much better than the angels, as he hath by inheritance obtained a more excellent name than they." (Heb. 1:4)
The JWs also attempt to use 1 Thessalonians 4:16 for their support, even though the name Michael cannot be found there: "For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first." The JWs conclude that since "the Lord" descends "with the voice of the archangel" that the Lord must be the archangel Michael. Using the same faulty logic, however, we could come to the conclusion that Jesus is God, since Jesus is described in 1 Thes. 4:16 as returning "with the trump of God". Surely the JWs don't want us to believe that Jesus is God, do they? The very logic they use to prove that Jesus is Michael also disproves the very thing they are trying to prove!
I hope you have found this helpful.