The reason is probably because rental cars are often used by visitors and tourists and so some thieves and robbers are more likely to target them. "recommend" is a verb which is often used in the subjunctive mood. The relevant structure is : recommend (+ that) + person + base verb e.g. I recommend you eat less chocolate (no difference in spelling) e.g. I recommend that your friend study English. (the final -s is lost) This structure is formal. In practice, the only difference with most verbs is that the third person -s disappears. With the verb to be, the subjunctive present form is "be".