What happens when that database fails? Are you OK losing some data, or do you want the data to be synchronously replicated off the machine and be available somewhere else after failure? Distribution isn't only about scale, it's also about availability.

What happens when that database loses some data? Do you want an up-to-the second backup, or point-in-time recovery? Or are you OK restoring last night's backup? Distribution isn't only about scale, it's also about durability.

What happens when you need to run an expensive business process ad-hoc? Do you want it to be easy to scale out reads, or to export that data to an analytics system? Or are you OK building something else to handle that case? Distribution isn't only about scale, it's also about flexibility.

What happens when you want to serve customers in one market, and make sure that their data stays local for regulatory compliance reasons or latency? Are you OK with having separate databases? Distribution isn't only about scale, it's also about locality.