That's not an inconsistency but rather the only way to reliably wipe user data. It would be completely broken to attempt wiping data by zeroing the userdata partition. That wouldn't get rid of all the data from the SSD even with secure erase commands for overwriting it.

A modern SSD has both static and dynamic wear leveling. An SSD redirects writes to the free blocks with the least wear and also moves around used blocks to free up the least heavily written parts of the storage. An SSD with a proper whole drive secure erase implements it by securely wiping keys.

You made an inaccurate attack on GrapheneOS and included a personal attack on the founder of the project with no basis too.