Expandable storage is pretty useful for someone who has a large library of music (especially a library in lossless formats).

I am in planes sometimes. I have no music subscriptions. I take RAW copies of my photos (which the phone does, that's the flipside of the mediocre processing for the camera) AND I play a bunch of games on that thing during flights. Not even phone games, although that too. Emulation is a use case for me.

Plus, internal storage is sold at a massive premium. Why pay hundreds to dobule my 256 gigs of storage when I can pay tens for a terabyte?

Oh, and this thing does hotswappable cards, too. So yeah, if you want to record hours of 4K video, then swap cards and record several more hours, you absolute can. For extremely cheap.

Why would you NOT want expandable storage?

EDIT: For the record, since you raise it, I would lose no data from this phone if I lost it. I get the same remote wipe options you get elsewhere, and everything that needs to stick around does get a cloud copy, including that music and games. But the bonus is I still get very cheap offline access to all that data without having to download it each time and a ton of additional storage for high quality originals of my photos and recordings before free cloud storage has their way with them. Not to mention easy ways to move data back and forth without relying on networking. Again, why would you not want that?

Why not have more storage on your phone for photos or music and then have that backup to a server? I encourage you to try to recover data from your broken phone. Much easier to read data from a unencrypted HDD then take a phone apart and try to read the bytes off it. You just keep all sensitive data on your phone's internal storage.