Speakers of Turkish generally build words with vowels from either of these exclusive groups:
aıuo
eiüö
You see? They could write "ä" instead of "e" to have all bright vowels dotted and mirror the symmetry. But because "e" was already available and pronounced like that in other dominant languages of the time, they stuck to it. No need to break conventions. This didn't work for "ı" because there was no corresponding letter in the Latin alphabet. So they loped off the dot from i and called it a day. A pragmatic decision. Except that the capital version had then to be dotted to keep the distinction. That caused a lot of headaches downstream.