Because the likelihood of an adult Saiyan losing their tail is extremely low, short of them not being some sort of moron who is just asking for it. That or whatever would have the ability to take their tail would also have the ability to just kill them. Keep in mind you all had knowledge of how they worked before Raditz, Nappa, or I showed up. Not every race does, or lived to tell the story. [Vegeta is well aware of what his people were like, and just how much damage they had done in the universe.

That question makes him hesitate. Does he want it gone? It wasn't really needed now days, not with him having Super Saiyan, and he had learned to adjust to having it gone. But... he had also missed it, even if he wouldn't admit that, even to himself. There had been no point to mourn over it once it was lost, it couldn't be changed after all. However, if he lost control...] It's not worth keeping if it threatens you. [And that's what it came down to. If he transformed, if he couldn't control that form, then the risk of what it could do to those on the train, to their kids, to her... it wasn't worth it.

Although, it raises a question, Vegeta getting caught up in those thoughts and tuning her out as he does so.] I wonder what would happen if I was in Super Saiyan when I transformed. Or Blue. [That was... he hadn't considered that. What would happen? The great ape form increased a Saiyan's power, so if he was already transformed before doing into that...]