They certainly do not crash as often as they do.
But if you bear in mind that data is flying around from hard disk to memory to CPU and back again at a very fast rate it is not surprising.
Data is also travelling all over the motherboard along BUS routes from graphics card and network card and USB card and so on. Again at an amazing speed.
Because of the speed of all this data, it only has to "miss" by a fraction of a second and it can all go wrong.
Also bear in mind your computer CPU is doing MILLIONS of computer instructions a second, every second it is working.
Also note that you have a combination of hardware and software, and data is being passed between the two all the time.
Also note that you could go out and buy all the components that make up a PC (motherboard, memory, CPU, hard disk, CD drive, graphics card etc) all from different companies, put them together, install some software, and it should all work.
Pretty amazing that it works at all in my book.