Since those Travis Mayweather & Harry Kim guys don't get a fair share of the action across their runs anyway. Better not to sign them up for seven years and have that option of releasing the actor, if the character is neglected.
Or if a character arrives at a point where he canīt possibly develop any further without becoming stale or boring.
Not bringing Picard back after assimilation, promoting Riker and keeping Shelby would have been a very interesting change to the dynamic IMHO.
Russel T Davies would be great "at the helm" of a new trek series IMHO.