Here's how it works. After yesterday's hearings, the three of them, along with Joe Manchin, went into a meeting together to deliberate. Why? Cowardice is a big thing. Nobody wants to cast what we call the "pivotal" vote. If they all vote the same way, then nobody cast the deciding vote. So, they were meeting to coordinate. Manchin might not go along, but he's nominally a Democrat, so who cares? From Flake's perspective, he might have wanted to get some kind of profile-in-courage award on his way out the Senate door, but only if it didn't actually do anything, diminishing the courage of the act. That would have required bringing Collins and Murkowski with him against Kavanaugh. Otherwise, he's pivotal, and he can't handle the pressure of being pivotal. If he couldn't get both Collins and Murkowski, he wasn't going to vote against "Brett," and without Flake, Collins didn't have enough cover, so that left her as a yes vote. That leaves Murkowski. She could cast a protest vote, but why bother? Remaining a Republican in good standing means standing by your rapist. Just ask President Donald Trump. Yeah, she can beat off a primary challenger, so to speak, but why do it if she doesn't have to? If you are staying in the party of rape, you stand by your rapist.
So, yes, Flake was always going to vote yes. However, yesterday's meeting showed us that Flake, Collins and Murkowski (and possibly Manchin) all wanted to vote the same way. It isn't the vote that is news. It is the sequence in context of the meeting.