Managing the marginal labor pool -- unskilled workers who earn minimum wage or slightly more -- is a perpetual problem in the fast-food and hospitality industries.
Energy costs, not surprisingly, also a major factor, and wage costs as well, and seeing increases in things like minimum wage, naturally, factor into that.
That way you wouldn't get the hard-to-justify (except to their mates) sky-high remuneration packages, while paying others at or below the minimum wage level.
As things are now, the restaurant pays a base wage (usually below the federal minimum wage level) and lets the servers keep whatever tips they receive.
That's 7 cents using the black market rate, which doesn't sound like a lot, but still amounts to about a half-hour of pay for someone who makes the minimum wage.