At least in part:
In every year from 1995 to 2008 (and probably before - I didn’t bother going back any further once I found this obvious of a trend), the batting average of balls in play allowed by the home team’s pitchers was lower than the road team’s pitchers. The two lines generally move together, so when league BABIP is up or down, it’s up or down for both home and road in proportional amounts. But the home line never crosses the road line. It gets close in 2004, when the gap is just two points, but then diverges back to the more normal five to 10 point spread.
Over that 14 year period, home team BABIP allowed is .295, while road team BABIP allowed is .302. We’re talking millions of plate appearances here, so a seven point spread is certainly significant. It’s essentially impossible for this to happen randomly. There is something inherent to being the home team that allows you to reduce the amount of hits you allow on balls in play. This is, for lack of a batter term, a home field advantage.