Strikeouts are increasing because batters are swinging and missing more:
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Behind the historical rise in strikeout rates is a rise in the rate of strikes in a plate appearance.
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Although the rates of both called strikes and swinging strikes have generally been increasing over time, the rate of called strikes in the last two seasons has dropped.
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Batters are more likely to swing in a plate appearance, and the rate of missing a pitch in a swing has also increased.
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Since batters are more likely to swing and miss, the rate of balls in play on swings is dramatically decreasing.
My hypothesis is that pitchers got better at catching the edges of the strike zone, with called strikes going up. Since it’s probably better to swing at those pitches than not, batters started trading called strikes for swings, with the hope that the swing meets the ball. All-in-all, probably a good trade-off against better pitching.
There are some very nice graphs at the link.
All the data does is show that the fraction of strikes increases in a PA. Part of this is fewer BIP on the first pitch and an increase in longer counts where endless pitches are fouled off. Added to this of course is the expansion of the strike zone that has led hitters to swing at more pitches out of the zone with 1 or 2 strikes. These pitches are more likely to be fouled off.
It all adds up to a big bore even more HR cant solve. 5+ minutes PA and periods as long as10-15 minutes without a BIP