While I think the compulsive apologizer is unaware of how often they apologize, it feels manipulative. For example, Friend jiggles against something, causing no damage, and says, "I'm sorry. I'm such a klutz". Then there's an awkward lull in which I'm supposed to say, "It's okay, you're not a klutz". After the thousandth such incident, it feels like the friend is simply fishing for attention and reassurance.
My apologizing friend had major surgery, and when she first woke up in her hospital bed, her first words were an apology to the people present. "I'm sorry, I hope you weren't waiting around a long time". And, of course, everyone had to effuse how it was no problem, we're all so concerned about you, etc.
I truly appreciate it when someone gently draws attention to my annoying habits. Few people want to be annoying.