Servers meant to provide a wide variety of computers need up-time more than anything else. Throughput and bandwidth are also highly important considerations, but it needs to be able to stay up and stay stable to effectively work. EXT4 is a file system dating back to the early days of Linux when it was still in its infancy as the basis of an operating system. As such, it has had time to mature and meet the concerns and considerations of those who work with Linux-based operating systems in a professional capacity.
XFS is comparable and sees a fair amount of use in servers and data centers. If a file system can stay stable and recover easily from catastrophic power loss, it is ready for usage in a production environment.