Auctions in recent years have resulted in higher prices paid for letters written by John Wilkes Booth than those written by Abraham Lincoln. What is a reason for this difference in price?

There is a surplus of letters written by Booth and a shortage of letters written by Lincoln.
Booth was a well-known actor; the demand for his letters rose as wealthy actors attempted to buy them.
There are more letters available for collectors to buy that were written by Lincoln than there are letters that were written by Booth.
Many people are more fascinated by villains and anti-heroes than by heroic figures.