What causes freak seasons?

I was wondering I’d freak seasons occur randomly or if there’s actually some sort of hidden underlying shift in attributes. On my Reds save in 23, Elly De La Cruz was a fairly decent to above average 3B (around 3 WAR) and then absolutely shot up one season to around 10 WAR, won MVP, and then returned to normal and even slightly regressed. Then, my shortstop went from being strong defensively with a ZR of around 7-8+ to a -.2 ZR for this season. I’m well over half way into the year so it’s not a small sample size, and his only rating drop was IF range going from 70 to 65. He’s also only 29 so I doubt it’s an age issue. It’s very frustrating too because I’ve perpetually had pitching issues which aren’t helped by playing in GABP, and I finally went and got a 3-4 WAR extreme ground baller free agent who is struggling to adjust partially because of fielding issues. Does anyone have any idea why these things happen?