:-D Hey Master J!
Welcome back to the forum.
You might as well as why do birds fly :lol: Sometimes I think it is more amazing that computers work, you know?
But as to your question, you could have a bug, you could have OS files that have become corrupted, you could have hardware conflicts...
I think the most important thing is to pay attention to what is going on When your computer crashes so the troubleshooting can begin.
You may want to make sure that you are doing your regular
maintenance, and keep a pad near the computer so you can write down what you were doing when the computer crashed, how long had you been on, etc., (really write it down, you won't remember otherwise), then you should either be able to communicate to a tech what is happening or perhaps determine the cause yourself.
TTFN
T