When the topic of BvS's box office comes up, the way the money was earned and when it made it is often ignored. I feel like people just look at the number and say "but it has a big number, that means people liked it." It made most of its money in its first weekend, largely due to the hype of Superman and Batman meeting on screen being an event and not on the merits of the film itself. It had its legs cut out from under it to the point a Melissa McCarthy movie did better one weekend, and while it made enough money to break even that's mostly all it did. That's why it has the weird reputation of being neither a flop or a hit. But the lack of repeat business indicated people weren't going to be fooled again, and they weren't with JL. Keep in mind most of the GA probably doesn't keep tabs of the behind the scenes stuff with Whedon, this was just a BvS sequel and most didn't bother to go see it.
The Snyder Cut happening is indeed unprecedented though, to the point where most of us thought hell had frozen over lol. It remains to be seen if spending $70 million on what is essentially an expensive ad campaign for HBO Max will prove to be worth it though.