I am sorry,but I forgot your name.为什么连词but不可以换成beacuse?

I am sorry,but I forgot your name.为什么连词but不可以换成beacuse? ----i am so sorry,i forget your name,but can you____me of yo did you eat your words,Billy?Sorry,dear.But I really forgot I am so sorry But I love I am sorry but I love you. I am sorry .your name __me. I am sorry but your watch is lost.中的but 是什么意思 But I Am Really Sorry什么意识 I AM SORRY.BUT IT IS TRUE. I am sorry to trouble you but.. I’m sorry,but i'have forgotten your name .Can you remind me Could I borrow your computer?Sorry,but I need it 回答为什么非要加but