This is perhaps because we mentally reserve the nominative case for subject heads only.

这可能是因为我们在心为题负责人保留了格。

The pronoun " She" is in the nominative case, marking it as the subject or giver.

代词“她”是格，表示它是语给予者。

And would anyone really say, " To whom do you think you're talking? " instead of " Who do you think you're talking to? " Speaking of whom, it is technically the objective case for the nominative who.

真的会有人说， “你认为你在和谁说话？ ” 而不是“你认为你在和谁说话？ ”说到whom， 从技术讲， 这是格who的客观情况。