Why does Marullus criticize the mob?
Is this answer sufficient:
Marullus criticizes the mob for wearing their best clothes and not their work clothes. He thinks they should be working, not celebrating.
Should I add that Marullus also criticizes them because they are celebrating Caesar even thought he killed the last emperor they used to honor?
Marullus criticizes the mob because on a workday, by custom, the worders should be wearing their work clothes (uniform) so that people know their social class and their skills and job.
Yes, definitely, add that he's criticizing them for celebrating Caesar.