Yes, the regular thief only hits one. But, the one who is robbed likely is insured, so it is then diluted onto all the customers of that one insurance.
Not always. And most of the time, not of the same amount. Also, the amount of paperwork involved even if something is insured is backbreaking.
But is it better to steal from everyone a bit and not all from one? Plus: a “regular” thief can hardly take stuff worth several hundred millions with him, and if he can, then the one who he stole from isprobably not ruined, or a fool not having that much insured.
Is it better to take a little from everyone or all from one? What is worse to rob, $100 from 1 person or $1 from 100 persons? Your right that a “regular” thief might not make out with several hundred millions, but the devestation is harder felt on a few though maybe not ruined. As for “insured” that is much of a crime also. Insurance is not free.