unless you use your fingerprint or face to unlock it (iphones and many androids have a key combo that quickly locks your phone and disables biometrics until you unlock it again with your pin or password. google it. useful in duress situations, but some manufacturers (in my case xiaomi) remove the feature. it doesn't prevent the stealing of all available data on your phone in case your attacker happens to own a cellebrite device and takes your phone away for a few hours (almost nothing can prevent that, except grapheneos), but it prevents quick in-the-moment abuse.)

It’s bigger on the inside.

Big wallet.

I don't use one myself for much the same reason as you. But I think a lot of people just need their phone and up to 3 cards (credit card, license/ID of some sort), so a wallet phone case isn't that much bulkier than a simple phone case. Yeah there's other things you'd put in a wallet, but they aren't strictly everyday carry things, so you can put them in a separate wallet or purse/bag and only take that when you need it.

For my mom I think she just likes a case with a front cover, and it happens to have space for cards so she uses it. So the "bulk" of it is a direct result of what she's after (the front cover), it doubling as a wallet is just a bonus.

And you'd have to get a new wallet any time you got a new phone.

When I first bought a wallet phone case, I was really excited to show strangers whenever I could. I understand this comic.