Why are the players on transfer limited to Four Star (30)

Whenever I look at the transfer market it is invariably limited to players that at best are four stars (30). Occasionally there are higher but it is a rare occasion. On the other hand if I bid on a player that is three stars (29) I find there are managers at levels 2 and 3 bidding. For the guys at level 2 this is a FIVE STAR (29) player. I've never been offered a five star player.

Is this a bug because I feel the game is becoming a bit limited with little chance of improving my team except by training.

Well, everyone on your level is probably in the same situation, if it's what I think and you are near or at the top level on your server... must be a new server.