As a general rule, I would only quote others 1) when your claim is liable to be met with skepticism by readers so an outside authority is needed to lend credence, or 2) when the quote itself creates a particularly compelling or masterful underscore or paraphrase of your point.
For a popular readership, quotes that are neither striking nor necessary create friction in the reading experience with no real value-added. Better to say the same basic thing (if you're not essentially plagiarizing) in your own words, thus maintaining a single style for the reader who is not used to switching between multiple styles. For scholars and bibliophiles, a mix of styles can be delectable, like spices in cooking or different sections in an orchestra, but for many popular readers it is seen as increasing the work involved and decreasing the entertainment value. After all, as a rule fast food doesn't have complex flavor, and pop songs specialize in having a single groove. So while you don't want bland, you do want to emphasize your style and maintain a certain degree of consistency.