Maybe to take down the details of their births rather than ask you (which seems weird and a hassle, but that's all I can imagine is in there that matters). Certainly, my midwives have never mentioned wanting to see the red book from my daughter, but they did ask about her weight at birth, gestation, how the birth went, a few other details that would definitely be in her red book. Maybe they think it's easier to do it that way and it speeds things along for one midwife to write it all in your notes while the other talks to you?