How is it nonsensical, were judging all of this in hindsight. Sometimes even when agreements are in place it doesnt turn out like they anticipated and a decision has to be made in whether to follow through with revisions or scrap it and start from scratch.
WB has been through this several times in the DCEU. Lest we forget, they signed and announced Michelle MacLaren for director of WW, skipping over Patty who was simultaneously in contention. Whatever clashes the studio had with the director, was found out early and they corrected early. Same thing with the multiple directors on Flash.
In JLs case, presumably it was only after the assembly cut where WB still wasnt pleased with the corrections from the guidelines imposed on Snyder from the start. This isnt uncommon. Disney went through this twice with Rogue One and Solo.
Its absurd to act as if WB just threw out hundreds of millions out there on a whim. I fully believe WB had difficult talks with Snyder post-BvS on what JL had to be changed to. When it still didnt work out, it was too late in the stages for them to consider starting over once again.
Of course, the blame is still on them for mismanaging. After all, Rogue One was in a similar state of revising and Disney still made it all work out in the end.