I wish I knew...
I've asked quite a few "experts" and they've all been unable to come up with a reason why it's occurring.
I take extremely good care of the blanks. Transport them very carefully to avoid any stress fracturing, chips, or cracks.
I don't recall the model number for the blanks, but they've all been the beefiest 11foot blanks available for spin fishing.
I only toss 3-5 ounce jigs and plugs.
I wouldn't say I'm an expert caster but I have no problem reaching the middle of the Canal when the tide's low. I'd like to say I have a pretty smooth cast. Maybe someone here can see if I have a funny quirk or something.
Here's a quick video of me casting...I'm the guy to the right, in the white tee.
Every rod I've snapped has broken during the cast. Never high strung it on a fish, or anything like that. Just a completely normal cast, and the blank just crumbles in my arms-awful feeling!
I snapped Lamiglas blanks 4 years in a row, and now after switching to a Dick's sporting goods special have had no problems.
Go figure and thanks for any insight,