George Lucas didn't really anticipate how popular Star Wars would become. They simply hoped for some modest success. Obviously Fox didn't realize it either since they let him have the merchandising rights and such. Back in that time-frame, sequels weren't really a thing, or if they were there were few and far between. The Summer Blockbuster was relatively recent as well with Jaws in 1975.
Other oddities about Star Wars: When R2D2 interfaces with a computer he sticks out a "probe looking thingy" and mechanically inserts it into a circular hole, and then mechanically rotates it. They said that it was akin to needing a key to open a door, and it needed to "do" something. Modern audiences would simply accept something like a USB stick being plugged in, no mechanical manipulation necessary. Also, when Vader asks Lea about the Death Star plans, he mentions "stolen data tapes". They've got ships that can go to light-speed, but they've got the DS plans on "data-tapes". Having them on "Data disks" would've made much more sense, but I'm not sure the floppy or anything like it was even invented then. The medal ceremony at the end is a bit odd as well, and it was put there because nobody was sure they would get a sequel so they gave the film an "ending" so it would be OK as a stand-alone film.