In the IA caucuses it’s not just a matter of going to the polls and casting your vote. You have to devote the evening to the caucus. Reps for the various candidates speak, folks in the caucus speak and/or ask questions before any voting. Fascinating, but it does pretty much take up the voters’ entire evening.
And, IIRC, the caucuses are ‘open’ which presents another challenge with idle Dems thinking they might impact the GOP caucuses results. That’s less likely to happen in smaller towns where they have to live with their neighbors who know their politics.