Why is the distance between peaks of the S&P 500 so regular?

I'm just learning about investing, so I apologize if this is obvious, but I was surprised by the regularity in the number of days between peaks in the S&P 500 and figure there's got to be an obvious reason for this. Does it have to do with quarterly earnings reports or something? Is this just my dumb ape brain pattern matching noise? I feel like the latter is the most likely explanation, but wanted to ask.

Thanks. The link is a picture showing the number of days between the last 10 peaks of VFIAX.

https://prnt.sc/gLEqjsfHX08y