Why would you expect the same, City want rid of Johnson, Wolves don't want rid of Jarvis.
If a player is realistically worth 5mil, then a club is desparate to keep him and doesn't need the money, then it usually takes above his worth to buy him, if a player is worth 5mil and a club is desparate to get rid of them and doesn't in any way need the money, you'll be lucky to get the 5mil.
Also Jarvis would be currently on a fairly low wage, while Johnson will be on a wage that is way above what he deserves, look at Ade and Spurs, the main issue is he is currently on a wage that he doesn't deserve and so won't move elsewhere unless he won't lose out on a penny.
Johnson could be all mouth, perfectly happy to stay and suck his wage out till his contract is up, maybe he'll leave and take a huge pay drop, you can't tell what way it will go.
Of course I'm talking in general, West Ham were willing to offer Carroll 90k a week and 20mil to buy him.... they aren't sensible.