Who writes on dried concrete slabs?

Besides the Mesopotamians of 2000 BC? Architects still do, put the name of a building or a famous prescription on the wall or on statues.

In Mesopotamia the art of table writing was scarce, mostly employed by the king and mostly involved in writing poetic law and religion, on the kings behalf.  It was still a vocal society, writing almost never in common use. The kings scribes put up the tablets for the king's poets to recite over the land.

There was no attempt to become phonetic, there was no attempt to spread the writing capability.  Commerce likely limited tablet writing to inventory lists. We needed papyrus to become phonetic. The medium influences he message.  Tablet writing was more a secret code for the king's operations, like phonetics was a foreign language dictionary for the Phoenicians. The difference is the availability of the medium, papyrus having the much larger bandwidth for mass communication.

So, low bandwidth tables worked better with a large, and complex map in the kings palace. One single location for the official grammar. The decoding is difficult, the poets become the intelligencia because of their ability to translate ancient tablets using the complex code.  But the message content becomes much richer. One could not put a complete Steinbeck novel on 15 tablets.

A quick summary from wiki:

Codices [binding flat pages]  were an improvement on the papyrus scroll, as the papyrus was not pliable enough to fold without cracking and a long roll, or scroll, was required to create large-volume texts. Papyrus had the advantage of being relatively cheap and easy to produce, but it was fragile and susceptible to both moisture and excessive dryness. Unless the papyrus was of perfect quality, the writing surface was irregular, and the range of media that could be used was also limited.
Papyrus was replaced in Europe by the cheaper, locally produced products parchment and vellum, of significantly higher durability in moist climates, though Henri Pirenne's connection of its disappearance with the Muslim conquest of Egypt is contested.[8] Its last appearance in the Merovingian chancery is with a document of 692, though it was known in Gaul until the middle of the following century. The latest certain dates for the use of papyrus are 1057 for a papal decree (typically conservative, all papal bulls were on papyrus until 1022), under Pope Victor II,[9] and 1087 for an Arabic document. Its use in Egypt continued until it was replaced by more inexpensive paper introduced by the Islamic world who originally learned of it from the Chinese. By the 12th century, parchment and paper were in use in the Byzantine Empire, but papyrus was still an option.[10]

Tablets, papyrus, parchment, paper.  The Indo European roots must have had some more primitive equivalent.   They at least had emblems, territory markers and the occasional road sign, but more, they must have had some support for the oral traditions for their stems to survive until today. I suspect a more musical system of stanza markers, emphatic points and a few phonetics as a poets aid.