These two statistics aren't directly comparable because the former is "against some [i.e., any] disease" and the latter is specifically the MMR vaccine. My guess is that in many developing countries the polio vaccine is the most administered because it's extremely cheap, extremely effective, addresses a very serious disease, and isn't at all painful for the child.
Another important childhood vaccine that would be covered in the 85% global statistic is the different variants of DTP.