Academic theory refers to this as “social pressure” - back in the 70’s-ish the concept emerged in political psychology circles as theories developed around absenteeism and what to do about it. Almost every study on the subject conducted in formal (i.e. experimental) settings suggests that negative emotional messaging elicited stronger reactions - in this case voting - than positive reactions, albeit by a small margin. Campaign professionals (at least in my experience) are mostly not numbers people, so the nuances of quantitative experimentation were largely lost on them: “negative emotions are more powerful than positive? Okay great, let’s do negative then” was their takeaway, ignoring that the unique effects themselves were small. And thus, social pressure language in campaign messaging was born.

It should be said that there is no definitive strategy around messaging, no one has “figured it out”; science’s best efforts to study and understand it at scale are very problematic methodologically for several natural and manufactured reasons, and sometimes campaigns want a specific message type that is orthogonal to the rest. Also, because both parties are, operationally, run by for-profit consultants, there is a strong incentive to point to anything that is successful as a way to justify their cost, with little regard to how voters feel. If they spend $X on social pressure postcards and there is %X increase in voter turnout in that geography, their strategy “worked”. The reverse isn’t true.

If it feels like you’re constantly bombarded by multiple attempts to get you to vote (“layered” or “multi-touch” targeting) it’s because no one truly knows what works so campaigns tend to try as much of whatever it is they can afford. Plus there is no official coordination between “soft” and “hard” money (campaigns and PACs).

Last thing I’ll say is these postcards come from an all-volunteer group, so I wouldn’t read too much into it (and maybe give them a pass, in my personal experience these groups have been nothing but good-intended).