ACT scores trail education outcomes by ~10 years, as students in school in the middle of a shift don’t get the full benefit from it - they’re often not included in policy changes for the sake of continuity (you may not be able to suddenly change the way you teach math in 5th grade).
The main changes to reading instruction were made around 2013, and math instruction in 2016. I wouldn’t expect a decrease in ACT scores 12 and 9 years later respectively, even when considering that it takes some time for instructors to master the new approach.
Indeed they are towards the bottom, but not "tied for last".
Talking about statistics, take a look at the "Estimated % of Grads Tested" column. the top 20 do not break 20%, while the bottom is near 100% with the exception of Hawa'ii.
As for % tested, states that don’t mandate the ACT tend to have higher performance in general. They don’t have as compelling of a need for the mandate, and they have many students who’d rather just take the SAT on its own. There is an effect going the other way though - if you don’t mandate the ACT, then students who don’t want to take any standardised testing at all…won’t, and so they won’t depress the average score.