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

这可为我们在心理上只为主题负责人保留了主格。

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

代词“她”主格，表示它主语或给予者。

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“你认为你在和谁说话？ ”说到whom， 从技术上讲， 这主格who的客观情况。