Let me try that: "my car is so stable, it always starts on the first try", "this knife is unstable, it broke when I was cutting a sausage", "elephants are very reliable, you can't tip them over", "these foundations are unreliable, the house is tilting"
Strange, it's almost like the word "stability" has something to do with not moving or changing, and "reliability" something to do with working or behaving as expected.
Languages generally develop to be more precise because using a word with 20 different meanings is not a good idea. Meanwhile, native English speakers are working hard to revert back to cavemen grunts, and so now for example "literally" also means "metaphorically". Failing education and a lacking vocabulary are like that.