Why VOO over SPY?

I'm curious to understand why some investors prefer the Vanguard S&P 500 ETF (VOO) over the SPDR S&P 500 ETF (SPY). Both track the S&P 500 index, so what are the key differences that make VOO a more attractive option for some investors? Is it the expense ratio, trading volume, or something else entirely? I'd love to hear your thoughts on this topic.