I like to paint minis and also prefer metal. I also like a lot of different periods/genres that may not be available pre-painted. I enjoy the creative side of choosing my own colors, modifying figures, etc. I can make things unique (probably not award-winning though!), putting my own stamp on my minis when I paint them myself. There's satisfaction in that for me.

Nothing against pre-painted. If your main interest is playing games then pre-painted may be the way to go.

It's all about the fun. :D For some of us the fun is in the building and painting, for others it's in the gaming, for others it's some of both.