Why is that so important? Your disk encryption key is certainly stored in memory for the duration of your session (which on Macs might as well be forever since they don’t need to shutdown), so anyone with your user password can gain access either way.
It is important because M1 is iOS-derived hardware and unlikely to keep disk encryption keys in memory that you or anyone can freely dump. And hardware attacks against TPM are both costly and hard to perform.
Also in case of travel or emergency it's much easier to just power it off. At the same time there is tons of ways how someone can steal your day-to-day lock screen password.
