There are large classes of companies for whom sales of less than say $50k or $100k just aren't worth their time. All customers will have the same sorts of problems, so the smaller customer are less profitable.
The smart companies that want you to call them for a quote do it to make it harder for less profitable customers to come to them, without being at all an impediment for larger customers (who would want to negotiate anyway).
The dumb companies that want you to call them for a quote say "Oh look, ADP does it, we should copy it!"
The smart companies that want you to call them for a quote do it to make it harder for less profitable customers to come to them, without being at all an impediment for larger customers (who would want to negotiate anyway).
The dumb companies that want you to call them for a quote say "Oh look, ADP does it, we should copy it!"