That's true, but the way they do that is in a way that requires minimal changes. In terms of the management engine, that means not including AMT module (software) but keeping the rest of the ME (hardware). After all, it also does some essential things like power management and the bootloader. Removing it completely would also mean re-implementing the essential functionality.
The best you can hope for if you want to use mainstream parts is something like me cleaner where the management engine is only there for the boot, but is disabled afterwards. Something without an management engine would certainly possible, but would be limited to niche products like the librem.