my guess. the left side must draw more current or the contact has less area. also over time the contact get corrosion which further reduces the area available for power transfer. very tiny aching occurs at the connection which erodes away the contact.
that's why I think dielectric grease would help.
I think math has the answer, not so much physics.
CONSIDER:
The left turn signal is on more than the right.
Think about left versus right turns, sitting at a light waiting to turn left versus a right turn. Right turns can be made on red most anywhere, left - only onto a one-way street. You will wait longer with the turn signal on doing left turns than right turns.
Ah, Mathematics, my old, best and most reliable friend.
