I also use a mouse for pixelart. Pixelart isn't exactly requiring the features that a tablet provides.
Yeah because the scale at which you can draw pixel art assets is usually small (depending on the style of the pixel art), it would be easier just to draw them using mouse.
That being said drawing with a mouse can be frustrating if you have no experience using one. When I started doing pixel art it was awkward and slow and I thought using a stylus would be faster. But as time went on I grew faster and faster at doing art with a mouse I haven't thought about getting a stylus in a long time. Although I could see how using a stylus would be more comfortable for people who are more used to working with actual drawing tools.