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Why did the Ionic alphabet become the standard Greek alphabet?

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Thematic map of Eurasia showing the approximate geographic distribution of Indo-European language families, each represented by a different color. Areas include Celtic in western Europe, Germanic in northern and central Europe, Romance in southwestern Europe, Slavic in eastern Europe and Russia, and Indo-Iranian languages in South Asia. Non-Indo-European language regions and areas of common bilingualism are also indicated. — Greek language Approximate locations of Indo-European languages in contemporary Eurasia.

The Ionic alphabet became the standard Greek alphabet primarily due to its official adoption by Athens and its subsequent widespread acceptance as a common, 24-letter script.12

Before the 5th century BCE, various local Greek alphabets existed, including the eastern (Ionic) and western (Chalcidian) branches. While these local systems were similar in structure, they featured minor variations. In 403 BCE, Athens officially adopted the version of the Ionic alphabet used in the Anatolian city of Miletus.231

This decision proved highly influential. Over the next 50 years, the Ionic script gradually replaced other local alphabets across the Greek-speaking world. By the middle of the 4th century BCE, it had become the established Classical Greek alphabet, valued for its utility and consistency.231