They still have contracts and other clubs aren't interested/can't afford them. Then in other cases, like Darmian, clubs simply aren't paying what United want. There's no need to offload a player and give other clubs a bargain if the player isn't a disruptive influence and has his uses.
That's ecause those rumors get clicks on pages and therefor ad money. Transfer gossip is mostly just that, gossip. It's rarely accurate. Going to a psychic might yield better accuracy.
The fact is we don't know what the transfer strategy is. Money is certainly being limited somewhat. Spending big one year might mean less the next year or spending big 2 years might mean less the next two years depending on what the goals are. Personally I don't think the club is in horrible shape personel wise. I think we can generally agree with Mourinho's assessment before the summer on what the club needs and those places haven't been filled. Transfer are however complicated, clubs and agents know what kind of money they can expect. You also shouldn't just buy a player just because. Settling for a player won't solve anything. I think the club has settled too much in the past windows and I'd rather they'd stop doing that.
