You can’t split up the MMR or the DPT combos in the United States. You can in France and Switzerrland that I know of. Why?? I don’t think there is an answer that favors children’s health. The “excuse” is so that the child doesn’t need more stabs.
I see a reason for whooping cough, measles, not much else, maybe mumps for boys.
Chicken pox vaccine is BS. My two sons had it, caught it in the same wave. The unvaxed son had pox EVERYWHERE but only felt sick for a day or so. I knew how to deal with the pox to stop itch. My other son, vaccinated, had only a few pox on his trunk, but was feverish and sick in bed for a week. He was 8 and the other one was 3. Kids should be exposed to pox in elementary age and get it over with for pretty much lifelong immunity. They know the immunity is only partial and very short term so they recommend boosters every few years for life. What 25 year old would remember to get a booster? And c pox is horribly dangerous as an adult. Bad vaccine.
Against that, though, is the cosmetic implications of pox to darker skinned people. One of my “black redneck” buddies got the chicken pox, and thereafter has had to use make-up on his face. The pox area does not come back dark, is the problem. What on a white person might look like freckle marks is major unsightliness on a black face. It could be worth remembering to keep up with vaccines, even if they had no other virtue, to avoid getting pox on the face.