Porque é mais um título cativante
Não significa literalmente .. como você apontou, mas o título para filmes como este é parte do pacote geral de marketing.
Na verdade, o título original era diferente.
The film was written as Teeny Weenies...[snip]..
As Teeny Weenies seemed to appeal more to a child demographic, the name was changed to Grounded to appeal to a more mature audience. That name was later rejected in favour of The Big Backyard.
Honey, I Shrunk the Kids, a line of dialogue from the film, ultimately became its title.