The keeper deadline is a community-wide event to make cut/keep decisions and lock rosters until the draft.
Having the keeper deadline on July 31 means the entire month of August is available for drafts.
It also introduces variance as roster decisions and preseason performance can affect the value of both players locked into roster spots and free agents.
This will not be a per-league option, but if you want to get in on the community conversation about keep/cut I would recommend requesting a Slack invite.