The thing is, LLMs can be used for something like this, but just like if you asked a stranger to write a letter for your loved one and only gave them the vaguest amount of information about them or yourself you’re going to end up with a really generic letter.
…but to give me amount of info and detail you would need to provide it with, you would probably end up already writing 3/4 of the letter yourself which defeats the purpose of being able to completely ignore and write off those you care about!