Vincent was a free agent.
And yes it seems they preferred Stock to some of what they had in hand.
I guess they have just seen enough of Ramos, though he's still pretty young. He wasn't going to make the team this past year out of ST (until Arano's struggles) and they kind of buried him the year before too. Had also become injury-prone (just like everyone else, but with less track record).
I guess he must be out of options now? In fact, a lot of these moves can probably be explained by that. They gotta save the spots at the bottom for optionable arms, which none of our late additions were (how we got them in the first place), and they can do better (and spend more $) for the one or two higher-leverage pieces.
It also suggests that one of Pivetta or VV is definitely going to be in the bullpen, if not both.