Exactly. At the time they didn’t have any cases before them on the issue. You can’t say how you would rule on a issue until that particular issue is presented to the court and base a decision on what facts and arguments are presented.
I think there are more factors involved.
One can see the charade by studying Roberts' concurrence, which resembles the Dershowitz whinge. The question of whether or not SCOTUS may properly assign a "right" was not the question. Dershowitz goes so far as to assert that SCOTUS had to wait for a state to ban abortion before it could get to that question.
Lots of ways to frame that point of view. I'll call it process over substance. It's possible to nibble around the real issue indefinitely, by taking things case by case. That's what Roberts would do - usurp power in one big go. Rather than give it up, pretend to give it up by shifting the legal analysis, conceding little pieces here and there, but never letting go of "abortion, via privacy, is a constitutional right therefore you must come to us with the issue every time the issue comes up."
Similar game on RKBA, but in terms of what constitutes and does not constitute infringement. Case law is psychotic on this issue - but SCOTUS just nibbles at the margins.
The other factor involved is the makeup of the court. If the court was majority liberal, or majority conventional (never get to the core issue, always retain power to the court or to the feds), and say flip ACB, then Roberts would have written the majority opinion, and Kavanaugh may have signed on to a dissent by Alito. In that case, Collins wouldn't say ANYTHING about having been lied to or mislead. And justices being people, there is a certain amount of go along to get along involved.