NECA would love to put 6" TMNT everywhere but they have no control over this. Playmates owns the US retail license for TMNT action figures at this scale. Originally NECA was only able to put this kind of product out in massive 1/4 scale or in very limited quantities as convention exclusives.
Randy has been dedicated and determined to find creative ways to jump through hoops and loopholes to bring these lines to retail: with specialty retailers like GameStop, and for mass retail (like Target), displaying the figures in a unique "collectible" section--located closer to movies, music, and electronics--distinctly removed from the toy aisle.
If they don't do it this way Playmates would see NECAs figures as competing with their kid-themed lines and shut it down. So if you have a complaint about being able to get your hands on these items direct your frustration, and comments to Playmates.