Practical effects aren't that much more expensive than CGI all things considered, they just take a bit longer to produce and to reset if you mess up the scene. 

As for why they look better, its usually because there are these little bits of movement caused by the scene itself, little bits of lighting being off, or just some extra motions that a real object makes that an animator forgets about that make it look better when its real.

UNless its that sonic the hedgehog live action thing. Did that get canceled?