Photoshop is chock full of tools and features that a pixel artist wouldn't care about, and they can get in the way. On top of that pixel editors tend to have features only pixel artists would care about: mirrored output (pick one or two planes on the canvas and your work will be mirrored around them), ability to define simple, finite palettes and quickly move between the 5 or so colors you're using often. Also the ability to tweak colors in your palette and have the image adjust automatically (ie replace all of a certain color with another one), but not force you into an indexed color palette. Ability to zoom in very close but still maintain a 100% view, etc.
Most also offer nice animation tools such as looping your animation in real time allowing for effective tweaking. Even other simple niceties like they are always hard edged, always scale with a nearest neighbor algorithm, having both the right and left mouse button be full fledged tools, etc.
The canonical tool was Deluxe Paint on the Amiga, and most tools still around today emulate it at least to some degree.
Most also offer nice animation tools such as looping your animation in real time allowing for effective tweaking. Even other simple niceties like they are always hard edged, always scale with a nearest neighbor algorithm, having both the right and left mouse button be full fledged tools, etc.
The canonical tool was Deluxe Paint on the Amiga, and most tools still around today emulate it at least to some degree.