Earlier there used to be a restriction on the maximum distance trains could be run without toilet facilities. If I remember correctly, this was 150km. Though many exceptions to this rule exist now (and existed back then as well), the rule is still followed in setting the schedules for some trains. That could be one reason for splitting a single service into 2 nominally separate services. Some MEMUs on the VSKP-RJY-BZA-OGL were also scheduled this way. This also lets them make a small amount of additional revenue by exploiting the distance/fare particulars.
This may not be the correct reason, but its as good as any other guess.