Part of the reason for the drop is that traders will have poured their summer profits into upcoming movies, which then become over valued. Around Labor Day, the market will start to realise that there isn't a $30 million opener every weekend, and prices of the rest of the year's releases will drop accordingly.
Another part of the reason is that trading activity is lower over non-summer. Students are back in school, fewer movies that people are interested in leads to less trading, etc
Profitability definitely takes a hit, but it will affect long-term investors more than short term traders. Timing and being active (not passive) is key.