With Lojack, the presumption is that the local PD will have at least two cars equipped with LoJack's Doppler RDF equipment. You'll see four whip antennas mounted as corners of a square, on the roof or trunk. Each car gets an "instant" bearing to the transmitter and if the two cars have good separation (which means they both must be out on patrol, preferably several miles apart) then you take the two bearings and look at the place where they cross.
But if you are one ham, with one RDF unit that you have paid out for (several hundred bucks overall) then you need to take the bearing, plot it on a map, move to another location, take another bearing (assuming the jammer is still active), plot a cross...and that's more time, energy, and money than most hams or clubs can manage to raise.
Also, if you are in a big city, the steel and masonry canyons create a lot of multipath, and simply getting a true bearing that isn't just misleading echoes, is not assured.
Best done in teams of two (one to drive, one to operate the gear) at the same time, so now you need four people, two cars, two RDF set-ups. Or, you need to keep going out night after night and trying to pin the jammer down. Again, more than most clubs or repeater operators can commit to.