There's also the fact that releasing a player would incur a termination fee and lost resources in terms of development. We also don't know what kind of money and playing time Payne (or his agent) is asking for.
The fact you just rattled off 3 players that we already have as cover for that position is probably a big reason. Regardless of whether he is better than them or not.
Do we really need over a quarter of our playing roster used up on 1-2 position/s on the field?
I bet that his has nothing to do with the club not rating him, it is more likely to do with finances and they see him as challenging for a spot that we have Gorrin, Riera, and Lia for already. To discard Hicks, Lia, Ridenton, or Rufer would involve a termination fee and lost resources in terms of development for the last two. Also, Payne (or his agent) may be asking for more money or guaranteed game time than the club wants to promise. After all, Payne has been facing release for a while and his agent would have been in touch with clubs and vice versa. The club has to weigh up more when signing a player than how good he is.