Why is the Tu-144 the only commercial airplane with canard configuration?
Short answer: Canards make most sense with negative static stability and high maneuverability. Commercial aircraft don't need either, so a conventional layout works best.

For a statically stable aircraft, the conventional layout gives most efficiency with sufficient damping. Static stability requires that the forward lifting surfaces create more lift proportionally to their size than the rear surfaces. Here is an answer to a related question.

You want the airplane to return to the original flight attitude if it has been disturbed, say by a gust or a jolt on the stick. This can be done by creating proportionally more lift with the forward surfaces (= the wing in a conventional configuration) than with the rear surfaces (= the wing in a canard configuration). Say the jolt pitches the aircraft up. Now the aerodynamic forces should change in a way which increases lift proportionally more on the rear surfaces, so the aircraft pitches down and returns to it's original attitude. By distributing lift the way I mentioned above, the same change in angle of attack on both forward and rear surface will create a proportionally higher lift increase on the rear surface, making the aircraft (statically) stable.

That requires that one of the (mostly) two surfaces is not contributing as much to lift creation than it could. You want this surface to be the smaller one of both, so the whole configuration can create as much lift as possible at a given speed. A canard would be a poor choice for a commercial airplane, because the big wing would now fly at a fraction of it's potential.

Once you shift the center of gravity back to improve maneuverability, things get different: Now the rear surface is creating proportionally more lift, so the smaller surface should go in front. Voilá, a canard!

Now add forward sweep, which will make the wing tips twist to higher angles of attack when lift is increased, and you get a really responsive aircraft (but need to be careful not to overstress it!). This was done on the X-29 and the Berkut.

As jwenting pointed out, the canard on the Tu-144 was not a control surface, but should be considered a detached slat of sorts. Also, by adding some lift ahead of the wing it allows to lower the wing flaps in slow flight, increasing the lift potential of the main wing while maintaining the location of the center of gravity and stability.

And while we are at it: The Piaggio Avanti has a canard, and a conventional tail, too. Here the canard helps to put the wing spar behind the cabin area, makes it easier to fly with a wide range of c.g. locations and to increase aerodynamic damping. This is one of very few examples in commercial aircraft of canards done right!