I watched "Be-Gwang" (The Be-Gwang), but I don't understand why it's considered a "warehouse movie" (spoiler free)

I just watched it at a local theater this evening...
Perhaps because the director's previous work was "Miss Baek"...
The characters have a somewhat gloomy and extreme vibe...
But as I watched, it wasn't boring at all and was quite enjoyable...
Also, the main cast—Ryu Seung-ryong, Ha Ji-won, Kim Hae-sook, Kim Sun-young,
and Kim Young-min—are all veterans, so there were no weak links in the acting,
which made it very immersive... Even Kim Si-a, who plays the daughter,
is a former child actor and acted very well...
I heard it was originally a 2021 film, so I couldn't understand why it ended up
becoming a "warehouse movie" (shelved film) for nearly 5 years...
It's much better than something like "Okay Madam 2"...