Jacob assembled his sons before his death to tell what would happen in 'the end of days.' (Gen 49:1) However, the Divine Presence was removed from him and instead, he spoke of other things, as related in the next verses.  

Jacob gave series of messages, each one directed at a different son. Although they were commonly referred to as blessings, their actual content varied. The words spoken to the first three sons were more like rebukes. Those said to the other sons, apart from Joseph, appear to be designations - assigning a different role to each one. (Judah for the monarchy, Zebulun for trade - Gen 49:3-27)

Only the final verse states that Jacob actually blessed all his sons. The Rabbis tell us that these blessings were independent of the messages mentioned in the previous verses. All the sons were blessed then, whether they were previously criticized, designated, or actually blessed.

Why did Jacob wish to reveal events of the future to his sons? And why did it escape his mind the moment he wished to do so?

Jacob appeared to be rebuking some of his sons, designating roles to others, and only explicitly blessing Joseph. However the future of Jacob's children did not seem to fit into what he said to them. Joseph (the "blessed one") was the father of two tribes that ultimately suffered a degrading exile under the Assyrian Empire, (around 720 BC) together with the rest of the Northern Kingdom. In contrast, Levi, who was severely rebuked because of his role in the massacre of the people of Shechem, fathered children whose descendants thrived, up to and including the present day.

Jacob knew what the future would be at the 'end of days'. But, unlike Moses, he was not allowed to reveal the unpleasant details described by Moses before his death, (Deut 32:15-43) which were also referred to as 'at the end of days'. (Deut 31:29) Why? Because the Israelites in Moses' days actively demonstrated their propensity to sin. As Yahveh told Moses after the sin of the spies: "The Israelites tested Me ten times and did not obey My Voice."  Numbers 14:22  

Unlike the sons of Jacob, the Israelites had to experience Yahveh's displeasure, and it was essential that Moses warn them that they could expect far worse tragedies if they continued to transgress the Torah.

Even though Jacob could not reveal the details of 'be-acharit hayamim ~ the end times', he knew that they would be highly unpleasant. He therefore thought to avert it by persuading the people to obey Yahveh and walk in His Holy Ways. 

Jacob's final messages to his sons aimed to bring out the best of their personality traits, with the hope that they would inculcate them in future generations. To one, he gave a sharp rebuke, to the others, he gave advice and words of praise and encouragement, and only after that, Jacob blessed them all together, showing that he valued them each for who they were, even though they were very different from one another. (Genesis 49:28)

Jacob showed all future generations that to "Educate (train up) a son according to his way"  (Proverbs 21:22) includes treating each child as an individual, recognizing his situation, potential and qualities, and guiding him in that spirit.