Why do written records limit how far back the history of a language can be traced?

Written records are essential for tracing the history of a language, but they limit how far back we can look for several key reasons:

• Limited Time Depth: Written records exist for only a small fraction of the time that human language has been used. Over much of the globe, such records are entirely nonexistent.1
• Lack of Linguistic Fossils: Unlike biological evolution, which leaves behind physical fossils, language leaves few traces. While some information about the vocal tract can be inferred from skeletal remains, this provides very limited insight into the actual structure or vocabulary of ancient speech.1
• Restricted Access and Intelligibility: Even when records survive, they are often limited to specific groups, such as the priesthood or administrative classes, and were used for narrow purposes like inventories or annals. Furthermore, many ancient inscriptions remain undeciphered or are difficult to interpret due to a lack of bilingual keys or because the underlying language is otherwise unknown.23
• Nature of Written Language: Studying dead languages is restricted to their written forms, which may not fully capture the nuances of the spoken language, such as intonation or colloquial constructions.2

Consequently, historical linguistics can generally only reconstruct language history back a few thousand years BCE.1