Major corporations are not paying exorbitant licensing fees to have checksumming enabled by default. In fact, for enterprises running things like vSAN, ECC DRAM, etc, database checksumming is probably nothing more than additional overhead.
Database defaults in general are a touchy topic. Whatever set of defaults are chosen will be suboptimal for almost any serious user. A far more serious issue is figuring out the actual behavior of a database in different configurations. For instance, Oracle's SERIALIZABLE transaction isolation level only offers snapshoot isolation.
You don’t understand the critical problem that checksums solve at the I/O boundary. PCIe has weak error detection and correction. To transfer your data from ECC memory to your favorite super-robust storage technology requires transiting the PCIe bus, where for a brief moment it becomes relatively easy to corrupt data without anyone noticing. This is the problem that can’t be solved any other way and why checksums are primarily done at the I/O boundary in databases. It is an issue seen in real systems.
PCIe v6 is intended to materially improve the integrity of data transfers but what we are using today is much worse.
