1. The length. Why read 40,000 words about a dead guy who did nothing to influence our country's government or culture? How about 700,000 something words describing the Persian War and the events that led up to it?
2. The amount of detail. Herodotus, do your readers really want to know about every single pit stop the Persians made on their trek to Greece? Do you really need to lay out the every position of the forces of each army and describe to us the tactical advantage of each position? Plutarch, do you really have to tell us every single detail about Cimon's (who?) education, childhood, goverment...
3. These books are BORING. And they don't try to hide it. Who enjoys reading about a primitive civilization that bickers constantly about a field or spot of land (Herodotus makes sure his readers know exactly which land they're fighting over every single time).
4. Lack of life lessons (my CW poetry teacher would be awed by my awesome alliteration). About every 55,000 words in the Histories, there is a good one-liner or thought-provoking moment. 55,0000 words is more than half my book.
5. Presence of better resources. There are hundreds of history books out there that will take the 700,000 words in the Histories and condense it into a nice, 10,000 word summary. And still gives you all the good one-liners.
6. You can just watch the movie, which gives all the graphic representation and powerful dialogue which the book DOESN'T. 300 is rated R for "rescue" to Great Books students slugging through Herodotus.
7. It's summer.
8. The new Twilight movie is out, and judging by the commercials, the special effects and sound mixing are dazzling.
July 2 update: 9. Herodotus and Plutarch were pagan writers but never in the Histories or Lives did I really see them describe their religion and why they follow it. There was a brief moment when Herodotus tried to describe the origin of the Greek gods (he said they were based off the Egyptian deities...weirdo), but never do they pay much regard to matters of philosophy or religion. The Histories and Lives are solely about the history of two civilizations and their people of influence (Greece&Rome in Lives, Greece&Persia in Histories). Very few times do either classical writers endeavour to provide commentary on their subjects. They just "lay out the facts". I would rather read a thought-provoking book on philosophy or religion than try to fill my head with knowledge of all the squabbles and wars a long extinct civilization had.