It's not complicated. Phones are getting too tall for some pockets. I have an iPhone XR (not the biggest phone out there), and sometimes I need to remove it from my front pocket to put on my shoes (out fear of bending it half). A folding phone allows you halve the height while still giving you a full sized screen. It's not that dissimilar from Apple eventually eliminating the top and bottom bezel to fit a taller screen in the same body.
There are a lot of downsides to this particular phone (smaller battery, last years processor, fewer cameras than the S20, durability?) but it will have its market. I don't think opening the phone to use it is a big deal (there was a time where flip phones outsold candy bar phones). Unfolding it when you're already needing to take it out of your pocket isn't an issue.... you could leave it unfolded when sitting at a desk/table (or in that weird half fold mode) for easy access.
The form factor makes a lot more sense than the Galaxy Fold which paired a mediocre phone (exterior phone screen too narrow) with mediocre tablet (mostly a vertical phone interface on a nearly square tablet).