They don't make the movie to never release it. They make it, realize it won't perform well, and then never release it so they can take the expense of making the movie as a loss and offset profits from other parts of their business.

I can't fully explain like you're 5, but I'll try and connect the dots the best I can. When Hollywood makes a movie, and this is VERY broad terms, they have a total budget for production, and then a budget for marketing/advertising. Let's call those expenses P (production costs) and M (marketing costs). They spend $P to make the movie, then spend $M to tell people the movie is out. The efforts are to generate $R (revenue).

When the studio does their taxes, it's pretty similar to what small businesses do: $R - ($M + $P) = PROFITS. The company is taxed on profits, the lower the profit, the lower the tax liability. If a movie does really well, then PROFITS are large, and means they need to pay the US government and state governments their tax liability.

Businesses can use expenses like Marketing to deduct from those revenues, and if you don't want to pay the government, then reinvest the money: buy new equipment, pay vendors, buy real estate, etc. All those things are deemed to move the economy, creating secondary and tertiary industries.

Now let's say one of these movies gets a screen test, and it does NOT do well. In fact, you're nearly certain you're going to not make a lot of $R, even if you spend a fuckton on marketing. You've already spent $P, so that's the expense. Spending more on $M to try and churn up $R may be a fool's errand, because the testing has shown it's a dud (or they just want to believe it's a dud). What do you do?

Rather than spending $M to have a total cash expenditure of ($M + $P), just cut your losses. Shelf the project, don't spend a dime on $M, and divert that money towards $P on other projects. You've already spent $P, and you can take that as a pure deduction of expense, since you spent the money to create something that never earned your business any money whatsoever.

Further, depending on how the company is structured, they could use those expenses to reduce the tax liability of other projects that DID make money. "The Batman" made $767 million globally, and the budget (probably $M + $P) was $200 million, so the tax liability for "The Batman" would be $767 million - ($200 million) = $567 million profit. "Batgirl" allegedly had a production cost of $90 million, so by shelving the movie, they could take that loss and reduce the profitability of "The Batman" to $477 million.

So they're not necessarily getting money back, but rather they're reducing the money they owe because of their successes by offsetting with the cost of their losses.

Beyond the scope of your question, I'll say this: I think Warner Bros' love affair with HBO Max and the future of streaming was a quick burst of passion and is now subsiding. They're taking streaming content like "American Pickle" off HBO Max, thereby reducing the opportunity to generate revenue and therefore use the past cost of production as a reduction in liability. I think the jury is out whether HBO Max was a good or bad thing when you consider the effects of COVID, but that's yet to be decided. I do think WB and HBO Max went too hard, too fast, to capitalize on the streaming world without fully understanding the economics the way Netflix already does.

Add onto that the immense amount of money spent in real estate deals by WB in 2018 and 2019, and you have a recipe for a business that may be struggling with cash flow problems at a time when the global economy is showing signs of crisis.