They happen quite frequently actually. Now they may not be visual except with a telescope, but, they are visible. Then there was 1987a in the SMC. Don’t give up! Keep an eye out in www.skyandtelescope.com or spaceweather.com. They post when someone finds a supernova in a neighboring galaxy. Then use your scope, or, find someone with one, to look at it.
Well I saw Hale-Bopp in 1997 and a total solar eclipse in 2017, so I’m not too disappointed in the celestial circus. That and three other comets, a few dozen meteors, one during the day, and one hitting the roof and holding in my hand later. Several lunar eclipses, and so on. I don’t expect to see everything that can happen since a human lifetime is less than a blink of an eye in the cosmological reference frame.