I admit that I have trouble grasping cosmic scales. Light years, parsecs, billions of years ... it’s hard to picture things at such scales.
But, having said that, if a star explodes, and we see the bright light for 6 months or so, that seems quite brief. Sure, with instruments we could detect fainter light over a longer time. I know that the nova itself didn’t start and stop over just a 6 month period. But, still, in terms of visible light seen by the naked eye, for a massive star to explode and just come and go in 6 months seems pretty counter-intuitive to me.
Cosmic scales. Think of it this way. If our Sun were the size of a pea the nearest star, Proxima Centauri would be 125 miles away. The Sun is about 860,000 miles in diameter. The distances are just impossible to really comprehend.
A Supernova continues to put out a lot of energy for a long time. But the initial event is extremely cataclysmic. There are a lot of very informative astronomy videos on youtube. Search around sometime and prepare to be fascinated.