Preregistrations are a vital part of science, and we support preregistrations in confirmatory research (which does not imply that exploratory research has no value). Many of the signatories already do preregistrations on a regular basis.
However, in the commitment we define what steps in research transparency we always will do. As we will not always preregister every study, we did not include it in the commitment. A statement like “We often will preregister our studies” didn’t seem to fit.