Marsh has a 3.2 WAR.
They might have hoped Hays would add more than just a platoon bat if he could get back to his previous form (2.5 WAR last year) but obviously he was not going to add that much production in two months. They also had to know it was a long shot that he'd truly thrive against RHP.
Really, it was probably just as likely Marsh would come back around to his 2023 numbers against LHP, given the chance, as Hays would do the same against RHP.
And Rojas has 0.5 WAR in just 264 PAs. He's almost certainly played like a 2.0 WAR OF or better since his early season struggles, even if he's not hitting or looking like a Gold Glover the way he was last year (when he put up a 2.5 WAR with just 164 PAs).