I’d argue that SF should never have "grown up." Look at the works considered classics today, like Heinlein, or even Star Trek. At the time of release, they were often dismissed as unserious (TOS famously had scientific blunders like planets at -290°C), yet they remain cultural touchstones because they prioritized vision over rigor.

SF used to excel at selling "dreams" to humanity. By trying too hard to be seen as "serious" or scientifically airtight, authors sacrificed the sense of wonder that allows for mainstream success. We traded mass appeal for academic validation.