Why does the Haggadah tell us that "Even if they are all Chachmim..." they are obligated in Sippur? Are ChaChamim excluded from any other Mitzvot? Do they not have to pick up a Lulav because they are Chachamim? Or read the Megillah?
Why would I think that the Chachamim would not be obligated in Sippur?
See עבדים הינו for direct quote.
The mitzvah of magid comes from the paseuk "v'higadta l'bincha b'yom hahu leymor", so you would think that the obligation was only to teach our children specifically, or only to teach someone who clearly did not know about or understand yetziat mitzrayim. This statement in the haggadah comes to tell us that when even the least-knowledgable person in the room is a gadol batorah, we're still obligated to tell yetziat mitzrayim.
Perhaps the paragraph is coming to teach us something about the nature of the מצוה of סיפור. Perhaps you might have thought the obligation is to simply recite over the story that occurred in Egypt. It is a set of facts to report. This would be limited. It would seemingly add nothing to those who know “all the Torah”. However, perhaps the obligation is not to simply recite a story, but to be involved in discussing the area of Yitzias Mizraim. This discussion can start with the basics, but will spring board into an array of topics (Hashgacha, prophecy, creation, idolatry, free choice, etc.). It is an involvement in an area of study. It requires questioning and analysis that enters you into infinite area of study.
See רמבן on אנכי ה for elaboration of fundamental principles the event of the exodus establishes for us.
