Confusing cricket

Cricket is one legacy of the British colonial rule in India that we seem to be relishing... Today on the occassion of the T20 World Cup Final, I again raise my often asked question, "Why is it that unlike hockey or football or tennis or badminton or table-tennis etc. the playing field in cricket has no fixed dimensions. Some playing grounds are large and some are small, some round and some even oval?" .....Would be gratefull for enlightenment.