I like to watch it for inspiration and to see how they do it. I guess it's similar to speedpaints (as someone who does art), I enjoy seeing how others do it and see their techniques and learn from them.
To be honest, I actually got a lot better at building from learning from speed builds.
OP, since you like watching LP's, I imagine you watch sim videos for entertainment. Speed paints aren't much for entertainment in my opinion, so I get why you don't see what's interesting about them. :D
CAS is less appealing since there's only so much you can do with it, but for build videos, there can be more creativity being used to make the houses looks unique.
