They are intentionally made to be different, even on the same kind of car. I think the circuits used to be made with high-tolerance (high-variability) capacitors to make sure they would come out differently. But now it's all computerized, and in fact I think they are programmed to drift a bit faster and a bit slower as they run!

Old hazard lights, like the ones in rows along construction sites, used to blink more-or-less in time despite not being manually synced. The lightbulb itself would act as a weak photo-diode, so when a neighboring light was on, it took a minutely smaller time to charge the circuit. Eventually they would sync up :)