Yes, there are lots of reasons you might want to do that. Having stand alone liquid cooling in an isolated subsystem lets you efficiently move significant amounts of heat away from the place it's generated (on a single IC perhaps) to a location that allows for easy dissipation into some preferred environment. Sometimes that's a couple of inches just to escape an EMI enclosure or to get away from other temperature sensitive parts. I can also think of good reasons to not want to connect to the vehicle's liquid cooling transfer medium directly: cost, complexity, reliability, modularity can all suffer. Of course, dumping heat directly into the vehicle's head transfer fluid is thermodynamically efficient, but for the amount of heat generated by this system it's probably not a big deal - it's on the order of the heat generated by a single passenger and a small fraction of the heat load the car experiences from just being outside in daylight. Dumping heat directly into the cabin environment or into the ventilation system after using an isolated liquid cooling system to move the heat outside of the electronics enclosure seems like a reasonable choice for a compact, high reliability system with the order of 100W/liter thermal density.