Triangles taste objectively worse. The acute 45° angles are not effective at retaining sandwich contents so you are just tasting plain bread.
By cutting orthogonally you create 90° corners on each segment, allowing a uniform distribution of delicious filling throughout each sandwich segment.
That’s just maths.
Obligatory plug for STAR Voting, not Ranked Choice Voting. STAR voting better avoids situations where voting for a preferred candidate can cause a less preferred candidate to win.