Why do people worship Lakshmi and Ganesh on Diwali

Diwali is suited on October on November month', Diwali or Deepawali is the new year time for Marwaris and Gujaratis. That is when the business men close the accounts of the old year and pray to the goddess of wealth (Laxmi Ji)  that the new year should we increase the business and take lot-of profit. Ganesh and Lakshmi were historically the principal gods for the merchants - given the Gods close profit  to wealth and happiness (shubh, labh). This tradition is now catching up in rest of All India and world .

Story of Celebrating Diwali :

One time Lord Vishnu ji and Goddess Lakhmi ji were having conversation in heaven. and Goddess Lakshmi was praising herself and telling Lord Vishnu, she is the most worship worthy in the world and by her grace and blessing, a  person can get a pleasures of this world and becomes richest and happiest  person. By hearing the self praising by Goddess Laksmi, Vishnu ji said  to her for reducing her ego, “You are having all the qualities and money, still  you did not feel the joy of your life, the enjoying your life with happiness and piece full  is the most important thing in this universe.”  than  Lord  Vishnu made Goddess Lakhmi ji for that type of human's become disheartened and in  this pain, she went to meet her friend Goddess Parvati ji. After listing the  problem of Goddess Lakhmi, Parvati asked her, “How can I help you?” Goddess Lakshmi ji polity with pretty smile  said to Parvati ji, “ Look, You have having two sons and if you could give me one son, you would still have one son and I could get the grace of life. So, in this situation you can help me out.”