It’s just the difference between Space Opera and Science Fiction!
Only in Space Opera can a hero armed with a sword overcome villains wielding firearms. Only in Space Opera does the villains’ fortress/spaceship/super-weapon have One Fatal Weakness. The heroes of these tales hark back to the idealised knights of the Arthurian Romances. Hetero-romantic asexuals bound by an Unbreakable Code. They adore their Lady Fair from a distance and perform Great Deeds in her name or for her sake, but they seldom if ever get it together with her unless Destiny demands it.
Science Fiction, on the other hand, was once described to me as a ‘literature of people solving problems’. The characters are closer to reality (even Roddenberrys’ intolerably nice ‘evolved humans’), so yes, dalliance, romance and sex are going to happen.
The most interesting take on this remains the case of Doctor Who. In the early years, and right up to the Great Hiatus of 1989-2005, the Doctor was an asexual character, harbouring nothing more than paternal or avuncular feelings for his various attractive female companions. Since the programme is designed as ‘family’ viewing, no surprise there! But by the 2005 reboot, kids had become much more sophisticated, and there had been a massive shift in attitude. The new Doctor had an immediate spark with his new companion, the feisty Rose, while his later incarnations went on to develop a long-term relationship with a woman who was his equal in every way -the wonderful River Song. Further developments were the pansexual Captain Jack Harkness, and the possibility of Time Lords changing gender. What direction the current (female) Doctor will take this in remains to be seen.