I hate to call it a trend. Maybe a phenomenon or trope.
But look at how many there are:
Spider-man: Gwen Stacy now Ghost Spider.
Pepper Potts now Rescue
Jane Foster now Thor, Valkyrie
Betty Ross now Red She-Hulk/Harpy
Peggy Carter now Captain Carter.
Karen Page is the odd one out. But she was a ex-junkie/porn star who gave up Matt’s identity one time.
But Elektra (Bronze Age girlfriend) is currently Daredevil anyway.