It's not just cars. Our house alarm had two clocks, one in the alarm itself, one in the display/control panel, and the two didn't talk to each other, not just for that but everything else as well, for example motion sensor names.
It's now in an e-cycling waste bin somewhere, replaced by an ESP32 I/O board and Alarmo in Home Assistant, at 1/20th the cost of the original PoS alarm.