WHY DO PEOPLE OFTEN MISUSE “THEN” and “THAN”?

Using then instead of than and vise versa is a very common mistake, which both native and non-native speakers make. But why does this happen?
Perhaps because both words have a very similar spelling and pronunciation. However, they are different in meaning.
Then means “after that”.
Example: He finished work. Then he went home.
Than means “ in comparison to/with” and is used mainly with the comparative form of adjectives and adverbs.
Example: I am taller than my brother.
We can also use than in phrases expressing preference:
1.I prefer to + infinitive rather than + inf
Example: I prefer to stay in rather than go out.
2. I would rather + infinitive than + infinitive
Example: I would rather stay in than go out.