"More Bored" Vs "Boreder"

I have a question about comparative adjectives.

I read that if an adjective has only one syllable we write its comparative form as: adjective + er, e.g. bigger and if an adjective has more than two syllables we write it as: more + adj + than. For example, more beautiful than...

But we don't do this with every adjective, for instance bored. Bored has only one syllable yet its comparative form is more bored instead of boreder. Why?

We usually add +er to one-syllable adjectives and adverbs to make their comparative form. However, we use more + adjective, when:

1. We use one-syllable part participle adjectives such as bored, creased, pleased, worn, etc. Even after ironing, the shirt looks more creased than the others. These shorts look more worn than the others because they’re the only pair without holes that i have!
2. We use fun, real, right, wrong. AI is getting much more real every day! This idea is more right than the other.
3. We are comparing two qualities. ‘I think that dress looks gold’ ‘what? It looks more black than gold!’ Wasn’t he brave in that fight? Really, he was more drunk than brave’ Interesting Structures - not be + so much + adj + as + adjective rather than He wasn’t so much brave as drunk. It was black rather than gold.