Actually, the conservatives do not believe that a rising tide lifts all boats. No conservative party sincerely believes that, nor, as far as I know, has even sincerely believed that.
Because to them, the point isn't that growing the economy makes it better for everyone, the point is that the economy must be made better for them.
Because to them, the point isn't that growing the economy makes it better for everyone, the point is that the economy must be made better for them.