And it's something that, if standards of voting privacy are sufficiently eroded, could easily emerge even without any big conspiracy behind it. Just think of something as grass-roots as spouses not being amused about a certain vote, that alone could have a huge influence on the outcome in some settings. This potential for casual coercion is why I even consider it an erosion of democratic values when people abuse absentee votes for convenience. A mild erosion, but an erosion nonetheless.
Electronic voting could maybe improve on the issue of casual coercion if they allow individual votes to be recast until last minute, maybe even with some mix of deadline customization/randomization (with silent failure if already past the deadline) to add friction to less casual coercion attempts.
Small scale coercion, however, is easier to execute and easier to get away with, hence the need for your private vote to be cast in a public place.