There are a couple of reasons - not least being that Alias took their line-smoothing algorithms from their $1000+ application for Sketchbook
And that their drawing tools dont need to spend time doing canvas interactions and lighting rendering.
But there are a few things you can try to improve the look in ArtRage.
First up, turn off the 3D lighting renderer with the <F5> key. If you're just doing 'digital' type sketching, you probably dont care about the paper texture and canvas interactions while you're drawing. If ArtRage is spending CPU cycles applying lighting and textures to your strokes it can miss mouse events that would otherwise be used to smooth your strokes.
Second, try switching between 'Precise' tablet mode, or no. (Edit menu, Preferences, Precise Tablet Mode (Not precise cursors!))
Some tables, drivers, or tablet PCs give better results if we use the sub-pixel sampling on the tablet packets, some give better results if we dont.
Thirdly, try the pencil tool with the 'Precise' option turned on. This is a more 'digital' type pencil. Also try the marker pen with 'Art Pen' switched on.
You can also try turning the paper roughness down to zero percent.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"