If I had to guess, the mold they used to form the interior foam had worn out long ago. I say that because in my experience in my professional life, molded products have tend to not fit right when the mold your using is worn out. That's what this was. The recesses for the sim cards are so shallow that they don't grip the sims properly so they continually pop out. The ones in the center are worse than the ones at the perimeter. Again, a sign of poor manufacturing. Would not recommend this product.