Why do later Etruscan inscriptions often show fewer written vowels than earlier inscriptions?

In the Etruscan language, the tendency for later inscriptions to show fewer written vowels is primarily attributed to a linguistic evolution where vowels in later syllables weakened or were lost entirely in writing.1

While the first syllable of a word typically remained stable throughout the history of the language, subsequent syllables often underwent reduction. For example, the older form lavtun ("family") evolved into the later form lavtn, and mutana shifted to mutna. This pattern of vowel loss resulted in the creation of complex consonant clusters, such as in the name elchsntre (derived from the Greek Alexandros).1

Some scholars suggest that this shift may reflect an "economical" spelling system rather than a complete change in pronunciation, implying that lightly stressed vowels may have still been present in actual speech despite their omission from the written record.1