Immobilizers had an order-of-magnitude larger impact on car theft than LoJack. It used to be relatively trivial to start a car without the keys once inside. Now (disregarding certain Hyundai/Kia models) itβs essentially impossible to start without the key.
Cars are stolen far less often than they would be otherwise partially due to technology like LoJack. Did you grow up in the US? Steering wheel locks used to be on every other parked car. Immobilizers and LoJack made them a thing you buy for your weekend classic car only.