What do you mean? Somehow others will know how you voted?
Having to fill out the card, then checking the party preference box, then having to hand it to two more people that look it over, while you have people waiting near you for their turn. The ballot pile for each party are right there on the table for everyone to know which one you took.
Outside of FR, I’m very private about politics. Around these parts it’s one less headache I need.