grammar

The first is correct. I'm afraid I cannot explain why.

ArchieWWThe first is correct. I'm afraid I cannot explain why.

That's because they are both correct. (that is, if they had periods)

The past tense isn't wrong, but the present perfect is generally preferable with since.

Are you sure you don't mean this?

Since my last blog, I have spent some time in the hospital.

The first one. Because of "since" you cannot use the past tense.

Who decided that?

People who created grammar rules decided that I guess. Maybe I am wrong, you know English grammar is not easy.

austere125riversPeople who created grammar rules decided that I guess. Maybe I am wrong, you know English grammar is not easy.

My point is that the second sentence is a perfectly good sentence. In fact, I could say that it is better because it doesn't contain the unnecessary word "have".
Do you speak British English?

Not all ! I am not even a native speaker but according to what I have read, we usually use the present perfect when we want to emphasize the action rather then the time of the event. I'm just a newbie in English grammar and I have found that US grammar rules are different from British grammar rules.

austere125riversNot all ! I am not even a native speaker but according to what I have read, we usually use the present perfect when we want to emphasize the action rather then the time of the event. But the problem with that is we might not agree on what we are emphasizing. So 'rules' like that are quite questionable.
I'm just a newbie in English gramma

I do agree that rules like that are questionable expect that much of English grammar rules are questionable. Most of the time you'll hear people saying "this sentence sound better" rather than showing a rule to follow.