No one is saying not to start Ranger; if you use an opener he's still the starter. And it's certainly possible they were so conservative with him in Game 1 to preserve the possibility of pitching him in relief again, which is no longer a consideration. But with another potential off-day tomorrow plus the chance to close it out they can also still afford to empty the bullpen.
RHBs hit him much better, and both Albies and Riley have an OPS over 1.000 against LHP (Acuna is actually slightly below that but not by much). Ozuna is .980. Even Murphy is close to .900. The odds of him going twice through the order are low.
But of course it would also be managerial malpractice if you put the untested Kerkering or the still-not-completely-trusted Seranthony into the 1st inning and they gave up runs. Let alone Walker who doesn't even get lefties out especially well and has a 7.04 first inning ERA. He should probably not pitch in this series but will maybe get his chance next round.
It will once again be hard to use Sanchez or Soto unless there's a slot against the bottom of the order so it would be nice for Ranger to face Olson twice. But not getting Olson out in Game 1 is what ultimately led to him coming out.