For someone to get my wallet out of my pocket, they would have to hope I am rich, and then proceed to mug me. If I wore this, they could first check how rich I am, then decide.
Phones are pretty advanced and widespread nowadays. Wallets can not just contain cash, but debit or credit cards. If you happen to have just exited your car, they may take that too.
And you'd like to add your Bitcoin Cash onto that as well? 'I'm going to take your car, your cash, empty your bank and oh I see you have Bitcoin Cash, I'll take that too'.