I agree runes like Norse, Anglo-Saxon, Irish were straight lines for the most part since they were easy to make. Irish Ogrham runes were just basic lines literally just lines. Norse Futhark was more complex but still all angles.
Ancient Sumerians in modern Iraq area used cuneiform. The cut tip of a reed was used to make marks in in wet clay which was quite a rapid way to write. There are even old practice tablets with scribblings of children in school learning to write.
The reason they still exist is fire. A wood building burned at some point and the fire caused the clay tablets to harden like in a kiln preserving them.
In modern Inda/Pakistan region Harappan culture also used clay Indus script but it was more elaborate and not as "wordy". It seems mainly clay tags to attach to goods to identify them.
The earliest surviving evidence of writing was not baked in antiquity, just dried clay. Some have been baked in the 19th century for preservation. Some of the clay tablets have indeed survived presumably due to fires that burned the building in which they were stored - there is even some evidence of unsent letters found in ruins with signs of burning.
But the reason we have very ancient evidence of writing is categorically not because they were baked in ancient times.