There are many reasons that make it attractive, They are massively less likely to get relegated than us, they are significantly more likely to be promoted than us. I know full well that we have started better than them but I still very strongly believe this is the case as do the bookies. There is the chance that ccfc could disappear completely, unlikely but it's a factor to consider.
He would be playing in front of crowds with about 16k sheffield fans vs about 1500 ccfc fans. Sheffield is a more fun city to live in than Coventry. Though it's easier to get to Birmingham and London from here.
There is much more positivity and alot less negativity around their club.
He will quite possibly know if it's possible we are going to lose baker/christie/clark etc and if we are that makes staying significantly less attractive
He could very easily get a massive payrise and it's not guaranteed he will be able to in the future. If he is 100% positive his great from is sustainable and down to being a fantastic talent then staying isn't much of a risk financially, however if he isn't 100% sure on this and if he thinks ccfc won't be able to keep up the great scoring record, that we might struggle in the winter, that we might lose his striking partner, that his own form may drop then it's possible he won't be a target for other clubs in the future. If he is at all unsure about his talent he should get the financial security from taking a massive pay rise and a 2 or 3 year contract.
I have no idea if he wants to leave, if sisu would sell, what the offer is if there is one, but if I were him and the payrise is significant and ccfc arn't willing to offer a contract that provides a big increase themselves then I would leave, it's the smart thing to do.
Those are all good reasons to go however, but your first point regarding they're expectations for the season, it has to be said the first two teams I expect to be promoted (and already have odds on) are P'boro and Brentford, possibly at a push Wolves, however that then leaves 3 other spots in the play-offs, Bristol City will be looking for an immediate return and have a much stronger squad then Sheff Utd, as stated before I think Wolves could be in the Play-Off's they have a strong enough squad to get out of this League, Leigh Griffiths, Bakary Sako and Zeli Ismail should they stay beyond on the window should be enough to get them in the play-offs with their squad. After that you are talking at least seven teams who are well equipped (albeit they all get through this current window) to go up and I do see Sheff Utd in that seven and ourselves, but I think there is more chance of someone else sneaking a spot than Sheff Utd.
Okay for this league that will be the biggest attendances you'll see however coming with that means a change of pressure, Callum Wilson has only just started to become a first team regular, is 21 and has only just started scoring goals consistently (Albeit we are talking about within five games of the new season) do you think he will;
a) Move to Sheff Utd and sit on there bench?
b) Be able to deal with a pressure in front of that big a following most weeks?
Albeit Sheffield might be a better place to live however at the moment Callum is playing for his hometown club, his friends from Childhood are in the same team as Callum and a move away at that age could unsettle a player.
The loss of other players is based on speculation, not concrete, however I think any from the likes of Ipswich would be dependant on whether Aaron Cresswell leaves and I have heard Mick McCarthy say he is not interested in selling him as they feel they have a play-off push in there sights.
Yes he could get a massive payrise from what he is on here.
More reasons he might not want to leave;
Pressley has Callum in his plans no doubt, however you have to say from what I have seen so far SP has kept the players in the right manner, expect this situation (shoudl it happen) to be the same, Callum has been in fine form but has the partner that has so far helped him every step of the way which is a big reason as to his five goals already this season.
Callum as good as I have seen so far is still unproven at 21 and for a club like Sheffield United they are going to want someone who can make an impact.
I have no doubt that Callum is a good player however at this time I doubt he will see any move where he can be promised consistent First Team Football as a step in the right direction.
