There really is a lot less attention on these special elections than the ones in 2017-2018. Democrats (and maybe Republicans as well) are a lot more focused on the Democratic primary and national politics.
The Democrats' relative powerlessness after 2016 was probably a big part of their success in special elections during that period as well. Trump in the White House, Republicans controlling Congress, and substantial Republican control at the state legislative level lead to extremely high turnout and attention/money given to races that might not have been given otherwise. Feeling like you have nothing is a powerful motivating force.
Now that Democrats have retaken the House and made modest gains in state legislatures (as well as focus being turned to the presidential race), these special elections are not seen as a high priority as they were in 2017/2018.
