I've noticed this too. Strangely there hasn't been much discussion about this in live commentary, by pundits, or on football analytics Twitter. I don't think there's one right answer, but I'd guess any of the following could be valid considerations for the corner kick taker:
- Run up angle: Given the position of the corner flag, players taking the corner are restricted to very particular run ups before striking the ball (especially when considering whether it's an in-swinging or out-swinging delivery), so perhaps players are trying to maximize their angle for delivery.
- Shortest distance: It sounds silly, but it's possible players are simply trying to get as close to the goal as possible so they don't need to exert as much effort to deliver the ball in. I don't think a few inches would make that much of a difference, but perhaps it's psychological.
- Better turf: In my experience playing, the turf (specifically for real grass) around the corner arc can take a beating from players taking corners. In-swinging corner takers traditionally place the ball on the endline right where it meets the corner arc (position D in the image below), so the surface can take a beating from multiple corners (especially in wet conditions). So naturally players might place the ball where turf is more in tact for the ball placement and where they'll plant their foot, so maybe placing the ball at the extremity of the corner arc improves the lie of the ball.
Image source: SaySoccer.org: LAW XVII - MECHANICS