But you have to do that anyway to be able to produce the correct capitalized version: an "English I" or a "Turkish İ".
The person you're replying to is pointing out that differentiating English-i from Türkish-i requires some other unwieldy workaround. Would you expect manufacturers to add a third key for English i, or for people with Turkish keyboards to use a modifier key (or locale switching) to distinguish i from i? All workarounds seem extraordinarily unlikely.
Yes, there are two keys, but their function is not to write the character as a "Turkish i" and an "English i". These keys are necessary because there are 4 variations, that need 2 keys to write with caps lock on and off:
Key 1 - Big and small Turkish "I": Caps Lock On: I Caps Lock Off: ı
Key 2 - Big and small Turkish "İ": Caps Lock On: İ Caps Lock Off: i
For small "Turkish i" and "English i" to be different characters, there would need to be a third key.