In the native message to DELETE a message or picture etc... you have to do a long press, then tap DELETE in the menu then tap DELETE agian in bottom of the screen then appear a little tab asking you: Move this message to the trash? And the alternative cancel or Move to trash.
In the Gallery don't appear the little tab in the bottom so...they are an uniformity and to many steps.
They could make it more simplified:
once you have activated the trash, you just have to long press and in the menu select DELETE and that's it or you can include in the option Move to trash.... reducing the steps makes things easier