Warning: contains spoilers for Spider-Gwen: Gwenverse #2!
Marvel has a serious and her infamous death in The Amazing Spider-Man #121 marked a turning point in Spider-Man's life and was one of the signs that comics were moving away from Silver Age-silliness that defined the previous decade. But the Spider-Gwen: Gwenverse series highlights an issue with Gwen Stacy that Marvel cannot seem to solve, no matter how hard they try.
The relationship between Gwen and Peter was a twist on the classic trope of a love interest pining for a protagonist's alter-ego instead of the protagonist himself, like Lois Lane in the early issues of Superman. Gwen liked Peter - when he wasn't being perpetually late for dates or get-togethers - but hated Spider-Man for, among other reasons, being responsible for her father's death (he wasn't, but Gwen believed it to be true). Unlike her father, Gwen never realized that Peter was Spider-Man, and died ignorant of her boyfriend's guilt over the matter.
Upon her death in Amazing Spider-Man #121, fans clamored for her resurrection and return, but Marvel has steadfastly refused to bring the character back to life. Gwen Stacy remains one of the terribly few characters outside of a hero's origin story (Uncle Ben, the Waynes, etc) not to return from the dead; her death is the biggest visible consequence of Peter's failures and a constant reminder to readers that superheroes are not infallible. But the fans' cries wouldn't be silenced, so Gwen Stacy returned to comics again and again - first as numerous clones, then as Gwens from alternate timelines and dimensions. The Gwenverse series in particular sees Spider-Gwen team up with a multiverse full of Gwen Stacy variants, all of whom have different and interesting personalities...which is why none of them are actually Gwen Stacy.
The original version of Gwen Stacy was a rather flat character; her biggest personality trait was her slight anger whenever Peter ignored her advances (she actually dated Flash Thompson for a time because of this). Gwen's personality was defined almost entirely by her relationship with Peter - an unfortunate when it comes to writing female characters in genre fiction (especially when the writers are male). Spider-Gwen, Thor-Gwen, and the other variants are interesting characters regardless of their relationships with others. They may share Gwen Stacy's name, appearance, and several elements of her backstory, but that is where the similarities end.
Upon Mary Jane's introduction in Amazing Spider-Man #25, fans demanded that Peter end up with her instead of Gwen. Stan Lee never intended for that to happen, but Mary Jane was a far more interesting character than Gwen Stacy and he (and the rest of the writing team) knew it. Writer Gerry Conway, who penned The Night Gwen Stacy Died, killed her in part because "...she brought nothing to the mix. It made no sense to me that Peter Parker would end up with a babe like that who had no problems." Marvel must keep Gwen Stacy alive (in the form of variants) to satiate fans who long for her return while at the same time keeping her dead to ensure Spider-Man's mistakes have consequences, and thus the company covers up Gwen Stacy's biggest flaw as a character: she never had a character.
