As everything in human culture, language is dominated by tradition, which is to say that there is a customary way of expressing oneself in any given language. However, tradition is always susceptible to change, and in language this is primarily due to ERROR.
Thus speakers who mispronounce words by breaking with tradition do so because of the IGNORANCE of tradition. For example, as has been documented on more than one occasion here, the pronunciation of the element -lived in the compounds “short-lived” and “long-lived” has undergone a change in contemporary speech such that the traditional vowel [ai] as in the pronoun “I” has been supplanted by the spelling-induced vowel [i] as in “icky.” This is simply the product of error.
Recently this deviation from tradition was brought to Y-H-B by hearing the phrase “in excelsis deo” in the Christmas carol performed by a local choir mispronounced such that the word “excelsis” was sung with the incorrect [ch] rather than [s]. This mispronunciation can often be heard nowadays in radio transmissions as well. ‘Tis the season to be jolly!