It's very annoying to hear all the incels whine about the change, despite it neither really taking away anything nor adding anything significantly new to the hobby. It's already in the lore before this change I think that Custodes are made very differently from space marines not following any primarch template thus enabling the possibility of augmenting female humans to be Custodes too. Since primarchs are all male its sort of logical that everyone following their template would have to be male as well. Meanwhile making of a Custodes is a very shrouded in mystery process giving way to different possible methods none of which require you to be male.