You gave the info's wrong!!!
Matsya, in this fish avatar, he killed a daemon who lived in Ocean! and it was a time for distraction, so he told Manu to take all the plants, and 7 Saints with him!
Kurma: It was not earth, and this didn't happened on earth, it was in Ocean of Milk, Vishnu took kurma avatar to support, Mount Mandara, with Vasuki wrapped around it, during Samudra manthan, the churning of the ocean of milk.
Varaha: Vishnu appeared in order to defeat Hiranyaksha, a demon who had taken the Earth (Prithvi) and carried it to the bottom of what is described as the cosmic ocean.
Narasingh:Vishnu killed a rakshasa known as Hiranyaksha. Hiranyaksha's brother Hiranyakashipu, greatly angered by this, started to abhor Lord Vishnu and his followers. To which end he decides to attempt to kill Vishnu by gaining mystical powers, which he believes Brahma, the chief among the devas will award him if he undergoes many years of great austerity and penance. Can you win a Atheist's heart, with few nice words? No, the same way was Hiranyakashipu, His Son tried to convince but, Hiranyakashipu didn't heard!
Vaman:Vamana taught King Mahabali that arrogance and pride should be abandoned if any advancement in life is to be made, and that wealth should never be taken for granted since it can so easily be taken away. Vamana then took on the form of Mahavishnu. He was pleased by King Mahabali's determination and ability to keep his promise in the face of his spiritual master's curse and the prospect of losing all his wealth. Vishnu named the King Mahabali since he was a Mahatma (great soul). He allowed Mahabali to return to the spiritual sky to associate with Prahalada (the demoniac Hiranyakashipu's pious son, also a descendant of the demon race) and other divine beings. Mahavishnu also declared that Mahabali would be able to rule the universe in the following yuga (age).
Parusuram: He is famous for killing the Haihaya-Kshatriyas on the earth 21 times for their Ahankara (pride and arrogance). He wanted to spread and preserve the Vedic culture on Earth .He wanted this earth to stay alive for Jeev shrishti like birds, animals, trees, fruits & whole of Nature. He explained that Dharma of Raja was to spread Vedic life & not empowering its praja through kingdom.
Rama: Rama was born to kill Ravana, He was an ideal king that, for his people he left his wife, not bcuz he was interested in king ship, but to show how a king should be!
Krishna: Arjuna is a warrior, he wanted to run from battle field, so Krishna enlightened him by, saying, that soul is untouchable, indestructible, it has no birth nor death, the mortal body is temporary! besides kauravas cheated pandavas, they went in Adharma!
Kalaki: Your not sure, if we will have automobiles, there maybe a war and world may loose everything, even if we have automobiles, wat if God takes a Horse?
So you gave everything wrong, you did not understood the vedic principles!!