It's entirely possible that the issues that plagued the airline during the spring & summer might have spawned a very progressive program to reward people for sticking with the company, but United held back when it became clear that AA wasn't having much success with their poaching program, and Delta for all intents & purposes has ignored United entirely.

Every day they delay is another day for incremental improvement in United's overall operations, and another day to consider that small things like meal service order might offset far more expensive changes to their FF program.

In general, unless the changes are going to be very positive, there's nothing in it for United to announce early. Why give people a chance to react & flee if they see something they don't like?