San Francisco 49ers fans aren't the only ones wondering what happened to their team this offseason. General managers, personnel directors and coaches around the NFL are wondering, too.

"I have never seen anything like this in the current era of football," one GM said.

Watching veterans Justin Smith and Patrick Willis walk away from the game was one thing. Having relative youngsters Anthony Davis and Chris Borland also retire was another.

"It's crazy," a personnel director marveled. "You just don't see a mass exodus like that."

Those weren't the only high-profile departures. Jim Harbaugh and most of his coaching staff are out. Frank Gore, Michael Crabtree and Mike Iupati left as free agents. The team even traded longtime punter Andy Lee. It's a lot to digest, but as the aftershocks from this offseason begin to subside, the footing beneath the 49ers isn't as tenuous as it has seemed. I count five reasons why a big drop-off should not await the 49ers in 2015.