Explaining? Stars go supernova occasionally, there’s your explanation. There doesn’t need to be further cause or intervention behind it.

Stars don’t just randomly supernova. Stars have extremely predictable lifecycles. It’s hard to believe a warp-capable species never made it past a 19th century understanding of how their sun works, especially given how fundamental the underlying principles are to our own ability to observe and understand the universe.

It’s a plot hole in ST '09, though I agree that maybe it is best ignored unless they can come up with a truly compelling explanation.