Vinepair has an excellent article covering all the issues that surround beer freshness–which despite a growth in interest for aged beers, is still a damned important factor for almost every style.

There’s some disagreement over who bears the responsibility for old beer. Breweries are legally mandated to contract third-party distributors to sell their beer to retail stores and bars. Once this Reverb left its Missouri birthplace sometime in late 2013, Boulevard had very little influence over where it ended up—or when it got there.

That’s a big part of it.  You can’t really blame brewers for anything you find on a shelf, especially if they’re not even in the same town as the store where they might have reps that check up on stock.

The last bit of this piece is sort of a call to action.

If a beer’s out of date, tell someone: the store, the brewery, social media. And use extreme caution when dealing with breweries that refuse to provide any hint as to when their beer was born.

Definitely.  And if you keep seeing a lot of out of date beer on the shelf without some kind of acknowledgement (a heavy discount for example) then find a new shop.