Most, if not all, of these images are taken during a bright moon.
Narrowband imaging is a very useful technique that allows detail to be seen in objects that otherwise could not be detected. The Hubble telescope uses narrowband imaging with it's "Hubble Palette" of three wavelengths of SII, Ha
and OIII applied to the RGB spaces, respectively.
Narrowband imaging also allows you to image when you otherwise could not, like with a full moon or severe light pollution because the narrowband filters effectively block almost all of the unwanted light, leaving only the object.