evolution - Is there any reason for the variation in mitochondrial DNA size?

Shorter DNA would allows easier synthesis, but more introns could allow for more different transcription factors to influence gene expression.

Human mitochondria probably does not need to be as adaptable as mitochondria in yeast, since the a human cell's environment tends to be more stable. This could provide a viable reason as to why human mitochondria does not need as many introns, but this is only how I imagine things. I have no proof or experience to validate any of this - its just a possiblility.