Why do companies change the name of a popular brand once established?

Perhaps there is a change in the formula, actually creating a new product and distinguish a new name applies.

Sometimes

It is for all countries have the same name. Cheaper for the packaging and marketing. Oil of Ulay became Oil of Olay, Jif became Cif. Today, most major brand products it sold in Europe.

Also

Update a brand or product for marketing to increase awareness to a new audience. While this may be counterproductive, not marketing to let everyone know that have changed the name!. If it is not broke do not need fixing!