Why is SPX more expensive than spy?

Could you explain why the SPX, often referred to as the S&P 500 Index, seems to be more expensive than its ETF counterpart, the SPDR S&P 500 ETF Trust, commonly known as SPY? Is it due to the inherent differences in their structure, or is there another factor at play? How do investors typically factor in these price discrepancies when making decisions about which to invest in?