Why is the Dai alphabet more like the Burmese alphabet of Myanmar and completely different from the Thai alphabet of Thailand?

The Dai language, also known as Thai, is the language of the Dai-Thai people. The Dai language is divided into three major dialects, the Dai-Tai dialect (western Yunnan, north-central Myanmar, and northeastern India, China), the Lanna dialect (southern Yunnan, northeastern Shan State, Myanmar, northern Thailand, northern Laos, and northwestern Vietnam, China), and the Siamese dialect (south-central Thailand, southern Laos, and northwestern Cambodia), which contains several subdialects under each of them, and which belongs to the Zhuang branch of the East Asian (Sino-Tibetan) family of languages. It belongs to the Zhuang-Tai branch of the East Asian (Sino-Tibetan) language family.

Burmese is the official language of Myanmar, and belongs to the Burmese branch of the Tibetan-Burmese language family of the Han-Tibetan language family. It is mainly found in the Irrawaddy River basin and the delta region. It is spoken by about 28 million people, and is also spoken in small numbers in Thailand, Bangladesh, and the United States. Yangon is the standard language of modern Burmese. Since Burmese is the official language of Myanmar, it shows that Burmese translators are still used in a certain proportion in practical work and life. Burmese is an important language in the Sino-Tibetan language family, in addition to Chinese and Tibetan, due to its large number of speakers, long history, and extremely rich written records. It is of great significance in the study of the politics, economy, history and culture of the Sino-Tibetan speaking peoples.

Thai, also known as Dai, is the language of the Dai-Thai people and belongs to the East Asian/Chinese-Tibetan Language Family. Thai is spoken by about 68 million people worldwide. The Thai language is mainly spoken by the Dai-Thai people in Thailand, Laos, Burma, northwest Vietnam, northwest Cambodia, southwest China, and northeast India. The Thai language is divided into three major dialects: the Tai Tai dialect (western and southwestern Yunnan, China, northern and northwestern Myanmar, and northeastern India), the Lanna dialect (southern Yunnan, China, northeastern Shan State of Myanmar, northern Thailand, northern Laos, and northwestern Vietnam), and the Siamese dialect (central and southern Thailand, southern Laos, and northwestern Cambodia).

These three languages all belong to the Sino-Tibetan language family, so there must be some of the same, and the Dai dialects around the world correspond to different Dai scripts, all of which originate from the Brahmi script. There are Siamese Thai (Thai), Lancang Thai (Laotian) and so on, which are not completely different, and all have similarities.