Here's why:
* The Germanic consonant shift happened in Proto-Germanic. This was a language spoken by the ancestors of the Germanic peoples, including the Anglo-Saxons, before they migrated to Britain.
* The shift was a sound change, not a written one. It affected the pronunciation of words, not their spelling.
* Anglo-Saxons used a runic script, not a Latin alphabet, during their initial period in Britain. This script did not have a standardized system of spelling like the Latin alphabet.
* The Latin alphabet was introduced to Anglo-Saxons later, during the period of the Old English language. By this time, the consonant shift had already occurred, and the spelling of words was influenced by their pronunciation, not the original Proto-Germanic sounds.
Therefore, while the Germanic consonant shift had a significant impact on the pronunciation of Anglo-Saxon words, it did not directly affect the spelling as it was not a written change.
However, the consonant shift did indirectly influence the spelling of Old English words. For example, the shift changed the pronunciation of words like "tooth" from *tōþ* to *tūþ*, which eventually influenced the spelling as "tooth".
In conclusion, the Germanic consonant shift was a sound change that occurred before the Anglo-Saxons arrived in Britain. While it did not directly alter Anglo-Saxon spelling, it did have an indirect impact on the spelling of Old English words.