Your "Every film Rachel Zegler has starred in has bombed so far", claim is not the bullet point you think it is. According to Wikipedia, Zegler's filmography in which she has a staring role is limited to west Side Story (2021) and Shazam (2023). She does have five upcoming film roles though.
As far as Gal Gadot, she has a more impressive list of films; but only a few in which she was the lead.
Would you have said the same thing about The Princess Bride after learning newcomer Robin Wright was cast? While it made only $31 million on a $16 million budget, it went on to earn much more in rentals. It considered to be such a classic hit that no one is willing to remake it.
The three films Ziegler starred in all failed at the box office so obviously she isn’t a draw.
Neither is Gadot. Anything she’s starred in after WW or has a prominent guest role in has bombed.
Before BvS, no one had a clue who she was even though she appeared in several films. That includes her easily forgotten character in the Fast and Furious franchise.
Then she pops up in BvS and first thing people said was “Who the hell is that and why the fuck is that flat-chested scarecrow playing the most iconic and voluptuous superheroine in comic history?!”
As for Wright in PB, no because that was one role and she has a small part in it. But she was pretty bad in it and is easily lost in a crowd.