"call our sales representatives" means they'll tell you if you call. i'm guessing you never call, because you don't actually want to talk to anyone, which is exactly what they're trying to do: filter you out.
Best way to increase margins when the perceived "worth" is variable and it's a seller's market. Not so optimal in a market where you as a seller are in a buyers market.
They'll make you offers going from most expensive to cheaper, also it's a filter in order to lure in people who believe the product has value. You could say is a subtle way of asking people if they value the product highly, basically asking people to name the price even though not directly.
Among plenty of other things