Something similar happened in English, where "you", a formerly polite form which contrasted with "thou", is now the common second person pronoun with no inherent politeness.

It's a kind of semantic change called pejoration. In a society which values politeness, people will use a word B which sounds nicer/more polite than the usual word A. Once everybody uses B, B will become the norm, and people will start using a new word C to sound polite. By now, using A will be rude.

Something similar happened in English, where "you", a formerly polite form which contrasted with "thou", is now the common second person pronoun with no inherent politeness.

It's a kind of semantic change called pejoration. In a society which values politeness, people will use a word B which sounds nicer/more polite than the usual word A. Once everybody uses B, B will become the norm, and people will start using a new word C to sound polite. Once C is being used as the polite word, using A will have become rude.