What’s with the differences in returns between S&P 500 trackers?

Hey all, just a quick question.

Looking at things like SWPPX, SPY, VOO, etc — they all track the S&P 500, but they also have returned slightly different growth over time. Do they not all track the same stocks and should therefore logically return the same amount? Is it just a difference in expense ratios? Slight difference in dividends?

Thanks