Sherlock comes back after the fall, only to discover that John has died.

Any or all of the following:

+ Mycroft didn't tell him because he didn't want Sherlock distracted
+ John's death was totally normal - he wasn't being a badass, he was just in an accident or something
+ everyone else (Lestrade/Molly/Mrs. Hudson/etc.) has more or less moved on because it's been a while. They're sympathetic and it's still sad, but they're not grieving anymore.
+ Sherlock's relationship with Mycroft tanks terribly because Sherlock feels Mycroft was totally heartless in not telling him immediately (even if it would have compromised the destruction of Mycroft's web)