Everyone was surprised by its success. Guiness called it a stupid and childish fairy tale (which it ultimately is - farmboy saves princess from the clutches of an evil warlord with the help of a wizard and a pirate).
The stupidest thing ever uttered by a movie executive was "Sure Mr. Lucas... You can keep the merchandising rights and soundtrack royalties." Which is why I side-eye any hate laid at the Ewoks and porgs as a ploy to sell merch; they were no more a ploy to sell merch than were the Jawas.
Other fits of financial brilliance were from Sir Alec Guiness (or more likely his agent), who opted instead of a negotiated salary to take .025% of ESB's revenues. His estate continues to collect money from it and his take from that movie alone is more than $100 million.