Because you need to ingest all that happened in the first testament which you have more than likely not been exposed to nor explored on your own. Without having understood all that happened prior to Yeshua is(forgive my simplistic equivalency) like watching the first and last 20 mins of game of thrones or Lord of the rings and claiming to grasp what the hell just happened.
The entirety of the first testament speaks to Moshiach's arrival. The story of Yosef is a precursor to his suffering at the hands of his own brothers. In fact, it is Jewish thought that developed the concepts of Moshiach Ben Yosef(suffering servant) and Moshiach Ben David(Warrior King).
Yeshua's first arrival was clearly Moshiach Ben Yosef. Why did his own brothers reject him? The father said they would, long before his arrival. He was not pleasing to look upon. It is written that he was very sickly, and crushed by the father for all his people had done. If you want to understand what they had done, the text is waiting on you to go find out.
Don't let someone else regurgitate it on you and make things up. You are commanded to go. find. out. You are plenty intelligent enough to pick up the Bible and begin reading Torah(first 5 books). Then read them again, make notes. Research. Explore. Then read the prophets, your mind may explode, many times. Then move into Psalms and the words of David's son and see how it all layers on and repeats itself and events. Use your G-d given intellect to see the layers and the obvious enlightenment. Don't let others do this for you, that is not fruitful. He is waiting on you.
If you want the text summed up in a lazy way in it's absolute entirety, I give you the words of Shlomo.
"13 Here is the final conclusion, now that you have heard everything: fear God, and keep his mitzvot; this is what being human is all about."
If you want to further discuss, just shoot me a PM. You'll get no BS from me. I'm an explorer, a disruption. As Yeshua said, he did not come to bring peace but a sword. He was no hippy. He came to turn father against son and mother against daughter. He came to disrupt.
Your job is to find out why. He isn't a vending machine. He is the eternal. He is Echad.