how to repair garage concrete threshold

I have a really badly cracked concrete floor at the garage’s threshold, looks like the previous owner just slapped concrete on threshold, and it has broken in pieces. What is the right way to fix it?

Also, most of the time I see that garage floor kind of naturally propagates beyond the threshold, up to 20cm or so, and I don’t see it in my case. Does it mean the floor is not correctly poured?

Thanks.