I have a question regarding the design and function of loading semi-automatic shotgu

[RandyD]

I have a question regarding the design and function of loading semi-automatic shotguns. Semi-Automatic and pump shotguns both have a shell carrier that has to be pushed up to insert a shell into the tube magazine. However, but they differ in that the semi-automatic, requires a carrier release to be pushed to lift up the carrier, but a pump action does not have a carrier release. I realize the carrier release also serves as a bolt release. Why is it that semi-automatic shotguns use a carrier release? It is possible to disconnect the carrier release so that the carrier can be moved, and still have it serve as a bolt release?