I didn’t get it either til I came across a Galaxy Fold demo unit at the mall.
It’s light, the expanded screen gives you lots of extra screen real estate without feeling too big or unwieldy, and when folded up you get a normal aspect ratio, at a thickness that’s comparable to other phones.

I never really felt like a tablet would be useful for me, filling the “gap” between a laptop and a phone with essentially a ‘bigger phone’ I’d have to charge and carry always seemed silly: I’d rather just keep using my phone instead.
But when you merge both devices into one, it works. It really is a ‘bigger phone’, with the benefit of being able to choose when you want to use the extra screen real estate without having to swap devices.

As someone who often tries to juggle multiple tasks on a phone*, I want one.
Shame they’re so expensive where I live. Looking at the used market, even the folds multiple generations behind are still too expensive.

*Side note: Stock Android’s split screen implementation is shit.
The floating windows Xiaomi and other OEMs have is light-years ahead, Google should be ashamed.