Because it is an iconic feature of London, known all over the world, in the same way as the Eiffel Tower in Paris, the Colosseum in Rome and the Statue of Liberty in New York.
well the clock tower is not open to the public but back then the most favorite places people would go to was the big ben clock tower.
Big ben tower holds the clock faces and mechanism of the big ben tower clock
Big Ben
The official name for the Big Ben clock tower is actually 'the Elizabeth Tower'. The tower has four clock faces. The name "Big Ben" actually refers to the largest of the bells in the tower. It is this that is heard striking the hour
it really doesn't have a name like Big Ben but people call it, "The famous clock tower of Zytglogge"
You're probably thinking of the Great Clock of the Palace of Westminster, which is in the Clock Tower (recently re-named "Elizabeth Tower"). This clock is often, but incorrectly, called "Big Ben". In fact Big Ben is the largest of the bells in the Clock Tower at the Palace of Westminster.
The Westminster Clock Tower, traditionally known as Big Ben.
None as it is not a Clock Tower, but the public entrance to the Houses of Parliament. St. Stephens Tower is often mistaken for the Clock Tower housing Big Ben. Big Ben Clock Tower has 5 bells in total.
The Clock Tower of the Palace of Westminster is the official name for what people often call 'Big Ben'.
Big Ben
Big Ben is actually the 14 ton Great Bell of the clock in the Palace of Westminster. However, people now refer (incorrectly) to the clock and its tower as Big Ben.
London in England - the clock tower is called Big Ben.