Data via the Baseball-Reference Play Index
In an insightful analysis today, Matthew Trueblood shows that the share of plate appearances thrown by left-handed pitchers is declining. As seen above, only a quarter of plate appearances have featured a southpaw this year, continuing a three-year downward trend.
The 70s and 80s were the golden age of lefties, who faced at least 30% of batters in every year save for the strike-shortened season of 1981. (Baseball-Reference does not have complete data prior to 1974.) The current rate of 25.1% would be by far the lowest since 1999-2002, when expansion may have made finding quality southpaws difficult.