You can have fractional-reserve only because the public cannot see any difference between money from M0 and M1. In crypto the public uses M0 directly. For now at least. There are some M1 constructs - at MtGox there were 'codes' redeemable for bitcoins, but they are not transferable between exchanges.
Hey, the public also use bank notes with unique serial numbers. That has no bearing at all on institutions who hold your assets for you, as they don’t generally let you audit them.