Modern commercial aircraft are "reliable" because they get hundreds of hours of maintenance each year. Car engines are reliable, but require regular maintenance as well (oil changes, timing belt, etc). But generally it's all the electronics which start failing (electric door locks, powered windows, etc) for a wide range of reasons. My BMW for example has had various electronic problems including a recall on the spark plug coils (talk about an old technology and they still can't get it right!) and various other electronic gremlins (one of which killed my battery every 5 days if I didn't drive it because the A/C sucked 800ma/h even when off).
Frankly, I've been in tech now for nearly two decades and if it's taught me one thing it's this: very very few people/organizations know how to make reliable software & electronics. Those electronics which have to be reliable (or people die) are very very expensive vs. your normal commercial/consumer electronics (your iPod for example). Even systems designed with reliability in mind can fail (Amazon AWS outages for example).
Now start thinking about the conditions and elements a firearm is designed to go through with minimal maintenance: moisture, dirt, sand, salt, harsh cleaning chemicals, shock & vibration, etc which can cause corrosion and in general wreak havoc on electronics. Cars and plane electronics can have a lot of weather sealing (which adds bulk and weight) which is isn't so reasonable in a firearm you are supposed to carry and hold with one or two hands.
Simply put, added complexity reduces reliability and significantly increases costs.
That said, the best safety is training and being responsible (storing them in a safe, etc). Teaching people to respect (not fear) and how to properly handle firearms is the best safety. That's why I don't trust "safeties" on my firearms and I treat them as *always* loaded unless *I* personally have just verified it's state because a safety can fail for a variety of reasons (poor design, abuse, poor maintenance, etc). I won't even trust someone else verifying it for me- I have to visually check it myself.
That said, there are some really crappy guns being made which nobody should ever own/buy, but they're cheap. I do wish there were some appropriate safety/reliability testing standards that firearms had to pass and each one was given a rating (sorta like how safety ratings are done for cars). California does this which sorta gets it right, but causes problems for smaller manufacturers (like Les Baer, etc) which make very high quality firearms as well as other problems. A federal standard would help here, but frankly, I don't think I'd trust the Gov't to do it well and so a lot of gun owners like myself are hesitant to support such a measure and instead prefer to do our own research.