The reason is simple, because "Tai" is not "Tai".

Legally speaking, it is impossible to substitute Chinese characters casually like the people. When signing a legal document, the judge will verify whether your name is consistent with your ID card, otherwise you will be asked to re-sign.

Even in the folk, you can't write homophones on relevant evidence (such as IOUs), and the other party will ask you to sign according to the words on your ID card.