So - a little insider industry insight here:
To echo what Cathy said, this is a result of the drought a couple seasons back - which we still have yet to recover from. Feed has been expensive, so it's expensive to fatten up the cows. Another problem with this is that beef has been leaner in general, especially the fattier cuts like brisket.
We're fluctuating between $3.75-$4.25/lb wholesale (packer cuts) - up from about $2.50/lb or LESS prior to 2012. It has seemed to stop climbing, but probably won't recover for a couple years, if much correction at all (as retailers adjust their prices from such a long-standing hike - prices may just stay where they are...the fix is in!)...
Also, if you're just buying the flats of the brisket - you're paying an even higher premium for that cut (upwards of $8/$9 per pound). When smoking a brisket, you should always seek out the full packer cut - but flats are useful for an oven-braised brisket.
Here's a fun fact - what do the butchers do with the point if they are selling just flats? Why doesn't anyone sell just the "Point" (fatty) cut of the brisket for making burnt ends? Well, it's because they grind that up in their ground beef - that part of the brisket has a lot of fat in it, and is great in ground beef... (we, in fact, make our burgers from 100% ground brisket - and it makes quite a nice griddle burger)
Smoke that $4/lb brisket for 16 hours, you lose about 1/2 of it to fat/water cooking off & trimming...not a cheap meat anymore like it was when BBQ was invented...But I'll be damned if it's not as good/better than a fine steak when done right!!