Reason number 1) Murray is improving on grass, he will want to push harder than ever for this title.
Reason number 2) Djokovic is going to make a massive push for CYGS and even though grass is a weak surface for him, top form Djokovic could test Fed on the green.
Reason number 3) Nadal's back.... I think this one speaks for itself given Fed-Nadal history at Wimbledon. Forgetting one freak result, Nadal can easily match Fed at Wimbledon.
Reason number 4) A year makes a lot of difference. Maybe 2012 was Fed's last massive effort in a Slam because he knows he hasn't got much left?
Reason number 5) Jerzy Janowicz.
1) is reasonable. Could happen. I have Murray as co-favourite for Wimbledon.
2) is unlikely. I don't think aiming for CYGS will make winning Wimbledon easier.
3) will cancel out 2. If Nadal's back, there'll be no CYGS for Djokovic. If Nadal loses RG he certainly won't win Wimby. RG is by far his best tournament. I guess we'll have to wait a bit more to see where he's at. And - of course - Fed is highly unlikely to play all three.
4) possible, but doesn't look this way. Sampras last push came after a year of poor results. He was ranked far outside the top-10 at the time. Fed is still going deep in basically every tournament he plays.
5) has shown nothing on grass yet.