But yeah, fligh companies do not think they are important enough to bother their customers over them. They do the bare minimum required, and if you don't want to pay attention, they don't care.
...apparently more people do need to hear them and pay attention, particularly to the part of "Always keep your safety belt fastened when seated" because I've seen plenty of news lately of violent turbulence and passengers being thrown around because they didn't pay attention and follow the instructions they are legally obligated to follow...which is why no personal injury lawsuit regarding unintended turbulence for an un-buckled in passenger will ever win, near as I can tell.