GFCIs offer fire protection as well as electrocution - if your circuit is run through just a breaker, and an Earth fault occurs such that, say, 10A flows through the Earth loop, that is a lot of power for starting fires.
For example, my friend’s house has antiquated electrics with no GFCIs at all. A live wire came loose from inside a socket and shorted against the corroded Earth inside, causing it to get hot. The loop impedance was too high to trip anything, so the first he knew of the fault was that the socket wouldn’t work and was hot. There was carnage inside. A GFCI would have tripped to indicate the fault, and prevented any significant power from flowing. That could have ended very badly indeed.