"I believe many online reference simply copied the name from OSM without reasoning." Then it still doesn't explain why no one used "Tit Sei Kau".

Since all current uses are "Dit Sei Kau", one of four things is true:

1. This peak has no English name, and "Dit Sei Kau" is not widely accepted. In that case, `name:en` is not necessary.
2. This peak has an English name of "Tit Sei Kau". If this is the case, please give some evidence of its uses (from someone other than you), since I can't find any on the internet.
3.  This peak has an English name of "Dit Sei Kau", both before and after your edit in 2019. Then, this changeset is wrong.
4. This peak has an English name of "Tit Sei Kau" before 2019, but your edit changed the general public's consensus and made people use "Dit Sei Kau" instead. Then, use the new name, as `name` is meant for the commonly used name, not the "correct" or "original" name. Remember that words are an artificial construction, and all names were made up.