It does seem to be a weird window for the preponderance of overpaid stars on offer. Gareth Bale is paid so much money that he may have overpriced himself out of ever playing at a top club again. Bale, Neymar, Coutinho, Sanchez etc., all good players who would probably be interested in a transfer, but most probably won't move because clubs aren't willing to pay the fee and/or wages.
Agent greed and or stupidity would be a factor in that. Try to get the best deal for themselves...errrr, their client, they successfully screw their client and themselves out of a pay day.