Why learn to sing? You can either sing or you can't - right? If I already have a beautiful voice, why do I need lessons? If my voice sucks, why would I bother?
The purpose of voice lessons is to optimise the process, improve the voice you have - (much like polishing a gemstone or cutting a rough diamond), discover and develop your instrument and to sing with a vocal technique that allows you to sing efficiently for longer time periods and repeatedly to avoid vocal damage. Thus, it stands to reason that the more lovely the voice, the more often you will be asked to perform and the more demands you will put on your voice- the more your vocal technique, good or otherwise, matters.
If your voice is less than lovely do not despair, if you are willing to put the effort in and practise diligently under the guidance of a good teacher you will be amazed at what you can discover your voice can do.
Singing is not about becoming famous or gaining the attention and admiration of others - these can be by-products of good singing but are more likely to be the products of good marketing. If you are developing your voice with patience and care, you will discover the ease at which you can sing.