I think it mostly down to where he is in the pecking order.
Currently above him as wingers:
Watson
Potter
Ashton
Steward (if say Brown or Atkinson at FB)
Porter (if not at centre)
Simmons
Then there's him & Murimurivalu who are probably considered similar, but Kini may be slightly ahead.
Obviously he's a talented finisher, but the all round nature of his game isn't considered quite as good as those listed above. For me all of the above are better than Saumaki under the high ball which is critical to our gameplan atm.
He was going into the PRC as one of the leading senior players there, and whilst I think he played well, he didn't "stand out" throughout the game.
You also have to think he got unlucky with the timing of his injury (whatever it was) he was named in the 23 to play Ospreys away, Simmons came in and has quite clearly moved up the pecking order since. Saumaki isn't going to pull away from a chasing May in the Gloucester game foot-race.