Using FLP to say that atomic broadcast is impossible is overly simplistic. In the real world, where people do use atomic broadcast/consensus in real distributed systems, it just isn't a problem.

FLP says it's always possible to not achieve consensus, but it says nothing about the probability of it. In practical systems, unless you have a partition such that no quorum of nodes can talk to each other, the probability of not reaching consensus rather quickly is effectively 0. Such partitions are rare in real systems (basically requires multiple data center failures or multiple fiber cuts). You are much more likely to run into other problems that affect your availability, like code bugs or failed isolation between some components.