why cant photoshop smooth lines the way illustrator does?>
Which way that Illustrator does? Illustrator can use the Smooth tool to edit paths. It can edit paths made with the Pencil tool by redrawing within a user specified distance, and the Pencil tool can be set to be more precise or more smooth. The Curvature tool makes very smooth curves some find easier to draw with, and PS has now adopted it. The Pen tool makes extremely smooth lines in both apps. AI has the Shaper tool that lets me draw wobbly geomtric shapes and they become perfect shapes, but heck, you can just use the Shape tool in PS. That was really for people on touch devices.
I'm sure I could come up with more vector drawing that helps us draw smoothly if I take a bit more time. In AI, we often go to great lengths to make our lines not smooth in order to appear natural. So what feature, exactly, do you want Photoshop to have that Illustrator has?