Nobody thinks it needs to be involved. They want it involved so the drive is automatically unlocked at boot, but inaccessible if someone removes it from the machine to try and bypass login (and in the future, if someone tries tampering). Especially useful in machines you want useable without being physically present.
It’s not cajoling anything, it’s a built in feature you configure, although Ubuntu currently goes out of their way to remove the support from some tools.