I haven’t seen this mentioned by anyone here, but the fact that these are suspected of being plates used for printing implies a paper-making industry AND an educated public.
Good point. There must have been a literate class, at the very least, probably analogous to many an ancient civ’; the Egyptians and the Romans both relied on quasi-literacy among the general population, iow an understanding of a relatively few symbols (number system in Roman times; the Egyptians had symbols for “enter here” on the temples’ public entrances), with a fair percentage of people who could read and sometimes write.
In the Euphrates basin, regular flooding led to a need for both surveying (math) and recordkeeping (accounting, then writing) to make sure people were able to stay on their property and cultivate it. I’d be surprised if something along those lines didn’t happen along the Indus as well.
Settled agriculture is the basis for civilization, and leads to larger, healthier populations, larger families, more leisure time, and the development of other arts and industries, as well as standing armies.