Why was Gretel & Hansel released in the 1.55:1 aspect ratio?

Osgood Perkins (the movie's director) told the following to Polygon:

How did the conversations with your cinematographer, Galo Olivares, go as you were figuring out the look of the film, particularly in the early sequences in the woods?

We started thinking of the film as having a prologue and the body of the movie, and we talked about what would be expected for the first section. Probably square formatting, not quite sepia, but some kind of Instagram discoloration that looks like it came from your phone. We wanted to avoid all this. We don’t want to do something that anyone could do on an app. So we shot in widescreen, almost looking like the extreme wide shots you’d see in Westerns, and made the rest of the film — the “present” — squarer in its aspect ratio… Basically, you marry yourself to someone who you hope has a taste compatible with yours, and I got really lucky with Galo. The fact that we literally speak different languages allowed us to find a new grammar rooted in the visual. What he was thinking and what I was thinking were often the same thing, but sometimes it was a surprise to both of us what the other person meant.

Consequence of Sound interprets it like this:

With the exception of the fairy tale prologue (which is shot in anamorphic widescreen), Gretel & Hansel is shot in a 1.55:1 aspect ratio by cinematographer Galo Olivares (Roma). This makes each frame feel like a page in a storybook.

Other reviewers, like the one from Mountain Xpress, note:

Perkins makes the most of his claustrophobic 1.55:1 aspect ratio and fills the frame with disconcerting close-ups and gorgeous wide shots of malevolent silhouettes in a woods awash in a red, Argento-esque hue.