Well, because that’s a false piece of reasoning (it’s like saying “spaghetti and tortellini should take the exact same amount of time to cook because they are both pasta!” without taking into account anything else about them. I think there’s a word for this — inductive fallacy or something — but my brain isn’t working well at the moment.)

The parabatai ceremony and the birth ritual are completely different. One is about birth and death, the other is about bonding two people and is enacted with runes, which the birth ritual isn’t (you cannot Mark an infant). Otherwise what you’re asking is “Why didn’t Jace come back with every permanent Mark he’d ever had, and all their effects, undone?” We know that didn’t happen. He came back with all his permanent Marks and their effects still in force. We know only one ritual was affected: a ritual (the only Shadowhunter one we know of) that *doesn’t* include Marks. We know it didn’t even occur to Jace it *would* be affected. It was a singular, non-intuitive piece of magic (and bad luck.)