Think of it this way. Each of the seven planets has its own nature and inclinations. Having, say, the Sun in the ninth house of God makes sense for him to be ‘happy’ there, because the Sun represents God, kings, and all righteous authoritative figures — just as the ninth house represents the place where God rules rightfully in the divine heavens.
Or, my personal favorite, Saturn, who finds his disgusting joy in the 12th house — the harshest and most malevolent house of all. The 12th house rules enemies, secret ones, also isolation, misery, secrets (most of which aren’t good), imprisonment, and destitution. Any bad thing that’s the worst of the worst probably falls under this house. And what does Saturn’s nature make him want to do? Anything and everything horrible. A GOOD Saturn will keep you safe, but there is always some stuff he takes away. It’s like “equivalent exchange” from FMA, only just like in the series, it’s never “equivalent”.
Anyway, Saturn rules everything that goes against the goodness of life. And so, he finds his wretched happiness in a house where he can conduct the most mischief.
Another one is Jupiter’s joy in the 11th. There’s one ancient guy who argued that the 11th house was the most fortunate of all the houses — better than the 10th — for his argument was that, essentially, “the 11th has aspirations to climb higher and higher to the peak — that is, the 10th house, the highest point in the sky — but the 10th house has nowhere to go but down.” This, along with the 11th traditionally being known as the house of the good daimon, fits Jupiter’s benefic temperance.
Venus, on the other hand, desires intimacy and all things pleasurable. Like good food and drink, and all things therein that relate to children. Games, fun, and merriment too. These things that she wants, fit the sphere of her joy in the 5th, which indicates children, physical pleasure, stuff like that. So, she is happier in there than in other houses.
What do you have to say about your sexual Mars?
https://youtu.be/dCrLMwDz5qE?t=23s