Don’t think anyone has actually bought a phone for the thinness since like, 2016, but also a case isn’t a decision of thinness. The people who use their phones without a case continue to do so because they like the look and feel, and those who use a case for protection will want it regardless of whether the phone is 5mm thicker.

I've got an Otterbox Defender on my phone. It's the only reason my phone is still operational.

I still want a user-replaceable battery though.