Clearly writing databases is not beyond the reach of of current development, since we have a bunch of them and they have been doing pretty well at serving production workloads for literally decades.

Writing 100% bug-free databases is probably not possible with current development tools, but it might also not be required. Every extra "nine" of reliability costs exponentially more, whether you're looking at uptime, durability or any other metric. At some point the extra costs just don't measure up to the extra correctness gained.