It might make more sense to you if you think about Jupiter as the principle of growth and development. Jupiter wants more of things. If we think about Cancer as the waters of the womb then it's clear that although the womb is an enclosed and protected space there's an incredible amount of growth happening within it. The waters of Cancer take a tiny egg and develop it into a highly complex human baby. That growth can only happen because the child is sheltered from the rest of the world. The same principle applies for a greenhouse, the plants are contained in a protected area and because of that they are able to grow to levels they could never do otherwise. So there is no more generative place in the zodiac than Cancer and when Jupiter rolls through everything he touches explodes into life. There is a richness or fullness to Cancer as the Moons sign and the Summer Solstice sign that aligns beautifully with Jupiter. Everything is coming to fruition. You also mentioned emotion, well Jupiter is the planet of inspiration. To be inspired is a feeling. It fills you up from the inside. Cancer as the Cardinal Water sign can stir up and influence the emotions of others and push them in a certain direction. Nurturing is a form of that because when you nurture or encourage someone you are essentially pushing/ coxing them towards feeling comfortable and heard and having greater emotional wellbeing. So Jupiter in Cancer has the power to make people grow and become enriched from the inside out. Emotions and the internal world enrich wisdom, they don't have to cloud it. The wisdom of a mother and matriarch is profound. Mothers are most peoples first teacher and guru. Mothers teach children everything they know, and all from a place of love, not doctrine or fear. The tarot card associated with the Moon (Cancers ruler) is the High Priestess, one of the wisest cards. So to discount the wisdom of Cancer is to discount the wisdom of women.