The simple reason was that ancient people were Nature worshippers and worshipped foremost those element/s which were of primary importance for their livelihood. Hence, the North Asians and European races hailing down from the regions where the severe cold and long dark days of the winter made Sunshine an invigorating and vital force for them, were naturally inclined towards the worship of the Sun.
The Middle East and African folk, of the regions of torrid heat, on the other hand, get relief from the torrid heat of the daytime and impetus to work in the evenings after sunset and with Moonrise,which makes them deify the Moon as the ‘Moon God’!
Of course, both races worship both elements, but for the former, AsioEuropean races, viz. Hindus, Jews, Christians and the Egyptian Pharaohs, the Sun God, called Vishnu, Jehova and Horus respectively, is their Primary Deity, while for the Arabs and Mesopotamians , the Moon, named ‘Sin’ by them, was their Chief God(whom the Muslims have adopted and call ‘Allah’), and was a masculine god,while the Sun or Shams, is his feminine consort. Athar or Venus is their Son.
The Hindu God Shiva, also called Chandrashekhar(Moon crowned Head), was originally a Mesopotamian God, associated with the Nagas, and was earlier regarded as the subsidiary male consort of the Supreme Mother Goddess of the Lower Indus Valley, but was later narrated as having married the Scythian princess Parvathy, following his acceptance and inclusion by IndoAryans as a part of the Brahmanical Aryan Trinity. That explains why Lord Shiva was the God of the Devas as well as of Daityas(Antigods), viz. Rakshasas, Asuras and Danavas, equally, but Vishnu was not liked or worshipped by the Daityas, as they regarded Him as a Traitor, following the incident of ‘Samudra Manthan’ (Churning up the Celestial Seas) to harvest Nectar (‘Amrut’)for gaining immortality, by both Devas and Daityas, and the subsequent (mis)appropriation by Him of the ‘Amrut Kumbha’, (Pot of Nectar) for the Devas(gods) alone by Trickery!
It is the Environment and Lifestyle which are at the base of the difference in the favoured planet or animal being worshipped by different Tribes, as stated above. The First Group of Aryans, before they came and settled in the Upper Indus Valley, around 2000 BCE, and later in the Indian subcontinent, were a Nomadic race, and hence had to depend upon female cattle like the Cow, the female Buffalo and Goat for their Milk, especially the Cow as it is a cleaner and more active animal, and the cattle of both sexes for their Meat, as they did not settle down long enough at any place for Agriculture or Farming. The Horse too was an important animal for them because of their nomadic life, for transport, while the Male Buffalo gained status as the Animal for transport of Lord Yama.
On the Other hand, the Dravidians were much earlier residents of the Lower Indus Valley, and led a settled and leisurely life by the riverside, so that they were the first ones to take to Agriculture, for which the Bullock was an asset for ploughing the fields, and thereby for creation of food, as also for transport of people and goods by pulling Carts, while the Bull was venerated as a symbol of Fertility and the Vehicle or ‘Vahan’ of Lord Shiva. Therefore, it assumed the place of importance among the Dravidians. For the same reason, the Elephant too became an object of worship in the personalised form as Ganapati in some farming societies where elephants were prevalent, and the elephant spirit had to be pacified in the form of a God for guarding the fields and crops by worshipping Him at the beginning of every auspicious occasion along with the mouse, which also frequented the farms. Snake worship, (namely, of the King Cobra, as it has a magnificent and awesome look), started as it was realised that it protected the fields from getting damaged by rodents and hence useful and valuable from the Ecological point of view. Fear of Death by its bite was also a factor in Cobra worship, which was done not only out of gratitude to it, but also to plead to spare human beings, their children and cattle from its ‘Wrath’!
In short, Hinduism is the Religion in which veneration of the different aspects of Nature and the Animal Kingdom as of service to Mankind, and manifestation of the Supreme Spirit, plays an important role!