That you will have to be too many things to too many people at the same time. By going 'niche' you can concentrate on a subset of the problems, while at the same time validating the method. Once you've done that expanding from your niche will allow you to capture the larger market much easier than if you were to try to start that way.

It also limits the exposure of your 'gaffes' to the audience in the niche.

Also, you ask opposite questions in your title and the text.