I was reading an article on ESPN+ about the decline in hitting.
One point - starting this year, all teams are keeping the balls in humidors before games. in the past, the Rockies did this at Coors field, but now all teams are doing it, and there is some thought that it is making the balls less lively. the rate of HR's hit this year is down noticeably compared to previous years.
other factors: starters are working fewer innings, so more bullpen innings, and more use of the slider.
a few excerpts:
Scoring has dropped, and it's almost entirely attributable to one big change from last year. This year's batting average (.234) is identical to last year's through 10 team games. On-base percentage is up .001. But the leaguewide slugging percentage is down from .392 each of the past two years to .380 this season. Accordingly, runs per game have dipped from 4.44 last season to 4.22 this year -- nearly a 5% decrease.........
Since 2015 -- a year in which fastballs made up a massive 56.8% of pitches thrown -- slider usage has jumped from 14.5% of pitches to 21.7% this year.
The slider revolution is a reliever-driven endeavor. This season, bullpen arms are throwing it 26.1% of the time, compared to 17.3% from starters. The one-inning, max-out culture of modern baseball practically invites it -- and the jump among relievers from 21.9% slider usage in teams' first 10 games last season is no accident. Sliders have generated whiffs on 36.3% of swings, higher than the fastball (19.3%), cutter (26.5%), curveball (31.4%) and changeup (33.3%).