All astrological principles were laid down considering kalapurusha. and mesh as standard lagan. even lal kitab gives important to this. mercury exalts in its own hose but rest of planets, they have to pruve their strength in thier enemies house, mars exalts in house of satrun its enemy. venus exalts in his enemy jupiter, moon exalts in venus sign (venus inimical to moon) …now jupiter spiritual planet has to pruve its divinity in house of moon bcoz moon or mind is biggest enemy in spiritualism. if one controls mind then only he can continue spiritual path. sun or aatma, have to control its ego hence its exalts in martian sign. satrun have to pruve its exellency in house of kaam hence it exalts its. and mercury budhikaraka has to pruve itself in house of enemy 6th. there may be other reasons too