Before you post a comment about Bitcoin fees, please take a little time and try out lightning. It's come an incredibly long way, it's very fast, and very cheap, and very easy using a mobile wallet.
You can restore from a backup surely? Unlike losing a physical wallet, which in most cases, means losing the cash it holds at least, but possibly getting things like your ID returned. If you lose your mobile, you will likely never have it returned, but any funds or accounts you have on it can be reinstalled on a new mobile.
Go tell 6M citiziens to back up their mobile wallet - how exactly is the key here.
The key is just a bunch of words which one need to write down with pen and paper and store in a safe place nobody can access.
One can imagine better schemes of course, to hide or share the secrets.