According to what Hamill said at Star Wars celebration (via Variety), the original trailer was also missing John Williams’ music, so maybe it didn’t really highlight the movie’s strong points.
Still, despite having a small release initially, Star Wars: A New Hope went on to be a big hit, landing subsequent theatrical releases and still making a mark on cinema today.
Luckily, it all worked out, despite the fact the trailer was maybe a little bit cheesy and even included Chewbacca wearing headphones.
This isn’t really a surprise, as it’s a rather well-known fact that 20th Century Fox didn’t throw in a ton of money to market the movie back in the late seventies.
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Mark Hamill Himself Panel Full - Star Wars Celebration 2017 Orlando