Here's the deal. If J&J filed a Chapter 11, the talc claimants could reject any plan that gave them less than they would get if the company were liquidated under Chapter 7 (since you've represented individuals in bankruptcy, I'm sure you're familiar with the requires for a cramdown). If the market value of J&J is $400B, or even half that, or even one-tenth of that, the market value number has already accounted for secured debt that would have priority over the talc claimants in a bankruptcy. Currently, unsecured claims against J&J are probably negligible compared with the talc claimants' claims, so ultimately a J&J Chapter 11 plan could be voted down if enough of the talc claimants didn't like the amount they were allocated.
The divisive merger process takes this off the table and allows J&J to dictate the terms of the settlement. J&J gave LTL an amount of money and all the talc-related liabilities, and theoretically, that's all that will ever be available to pay the talc claimants. And talc claimants can have the plan crammed down over their objection (voting to reject the plan would have no effect), because they will receive at least as much as they would receive if LTL were liquidated under Chapter 7.
So the bottom line is the Texas Two-Step allows companies to settle cases by fiat. J&J has literally said "we're settling all these cases for this much. The end." Imagine a divorce proceeding where the other side said "I don't trust a jury to be fair, so I'm giving you this much, and you get to see the kids twice a year--once on this day and once on this day.--and there's nothing you can do about it."