So, from the beginning, you admit you haven’t actually researched the question. Not a good place to start.
How do you know they’re personal? How much study have you put into Shakespeare’s life? Oh, wait, you admitted you haven’t.
Yes, this is known as imagination. You see, a writer often takes on the persona of a fictional character for dramatic effect. I once wrote a story that convinced one of the readers I was a 13-year-old girl. I’m not.
In addition, these are just interpretations of literature. You can just as easily prove that Shakespeare was a Martian or even Bill Buckner if you use the poems for evidence.
The biggest problem with the claims that anyone else wrote Shakespeare is that, in all these years, no one has ever actually produced any* actual evidence* to back up the claim.
Interpreting poems isn’t evidence.
Saying, “Shakespeare couldn’t know that” or “He couldn’t have felt that way” is not evidence – it’s mind reading.
Objecting to minor points about Shakespeare (usually with limited knowledge of him) is not disproving anything.
I guarantee that, whatever interpretation you choose for any of the sonnets, I can come up with a different one that “proves” something completely absurd about him. It’s all a game (and, I admit, it can be fun), but it’s not anything that can remotely be called “proof.”