Reasons:
1. 2018
The 2018 midterms had record turnout for a midterm, with both sides, especially Democrats, having a strong showing in terms of raw votes. I personally know a few people who didn't vote in midterms before 2018 but have said they are more committed to voting in midterm elections in the future. I just have a hard time seeing enough people who were politically engaged enough to show up in 2018 not show up in 2022 to go back to 2014 level turnout.
2. Trump will (probably) still be an issue
On the Republican side, you have a lot of voters who are determined to get him back in power any way they can; he's likely to be active on the campaign trail too and could help motivate the base. We saw in 2018 that Republicans had a strong showing turnout-wise (Democrats just did better), and I think a large part of that was Trump keeping his "cult" of otherwise disengaged voters engaged.
Democrats on the other hand may be able to carry over a bit of anti-Trump energy because of fear he could come back.
3. Extreme partisanship
This one is pretty self-explanatory. Trump Republicans generally absolutely hate the Biden administration and want to do whatever it takes to weaken it. Democrats for the most part really do not want Trump Republicans in power.
4. Democrats have fear too
In the 2010 and 2014 elections; notorious for being low-turnout red waves, there wasn't really much fear on the Democrats side. Most of the main things in the media as to why Democrats should vote felt inconsequential, far away, and purely political to the average voter. While Democrats did not want the GOP in power, there really wasn't a fear of them regaining power other than amongst extreme partisans and political insiders who were already likely to show up.
Right now however, Democrats seem to have been to keep up energy around issues of voting rights. When you make people actually worried their fundamental right to vote could be in jeopardy, you create political energy that reaches even people who otherwise may not vote in midterms a reason to show up. This could boost Dem turnout in states like GA and TX especially which have been in the media a lot recently
There may also be a whole media cycle on redistricting which could create more fear
Also, as I said earlier, Trump fear may still be there a bit
Ultimately, I'm not sure which side, if either will benefit from this high turnout. But especially in midterms, who shows up and who doesn't plays a significant role in the election outcome.
Love to hear your thoughts on what you think turnout will be like in 2022.
Democrats currently have the White House, House, and Senate... how would they be more excited to turn out next year when they will have had all 3 for two years and still not got most of what they wanted done?