Usually a brake system flush is part of a brake job. Since brakes are a wear item, they won’t be on the PM schedule, therefore the fluid flush would also not be on the schedule. $150 for a flush sounds high to me though, but you did say Los Angeles.
BTW, you always flush a brake system if you haven’t removed any of the lines. You don’t “drain and refill” as that would unnecessarily introduce air into the system requiring a bleeding of the system after.