Why don't pilots parachute from small planes that are in distress?
Mainly because in the situation that you describe, the airplane is perfectly capable of flying.  You don't need an engine to fly as airplanes are designed to glide without it. Part of every pilots training is how to land the airplane when this happens. 

Many of the same issues also apply in the smaller airplanes.  Unless the pilot and the passengers fly around with their parachutes on, it would be quite difficult to put them on in the confined space, in a high stress situation, and with the very limited time available.  Even if they did, untrained people are going to be hurt (probably quite badly) during the landing even if everything else with the jump goes well. (See my answer on your linked question for some of the things that can go wrong during the jump.)

You are also creating a hazard with the aircraft not being piloted and crashing into a random place on the ground.  All of this when the airplane could have just glided in for a landing in a field or on a road.  Most of these types of emergencies end quite well, and even a lot of the accidents will have fewer injuries and deaths than if people were jumping out all of the time. As an added bonus, the airplane can even be used again! 

On the other hand, a major structural failure that makes the aircraft incapable of flight could be a reason to jump.  This is extremely rare however, and even if one has a parachute in this situation it may be impossible to exit the airplane safely because of high G forces and the possibility of hitting the airplane as you are both tumbling through the sky.  

Some manufacturers are now building ballistic parachutes into the airplane which can bring the entire airplane down safely in these situations.  This is much more safer, reliable, and does  have a positive impact on safety in these extremely bad situations.  For just an engine failure though, I doubt that most pilots would even fire the ballistic parachute if there were suitable landing spots within gliding distance. 

My view is that you would have a far greater safety impact by requiring everybody in a moving car to wear a helmet.  Would it improve safety?  Absolutely.  Would people want to do it?  A few would (and perhaps a few do), but the general population doesn't want to be inconvenienced by something that is only a remote possibility.  The odds of a parachute helping you in a typical GA airplane is far more remote than the odds of the helmet helping you in a car.