I am very sympathetic to your situation. It just seems that like either the time should matter or it shouldn't.

Let's take Alice and Bob, who are both in the same class.

Alice has clinical depression, but on this particular Tuesday, she is feeling ok. She knows the material well and works through the test answering all the questions. She is allowed 30 minutes of extra time, which is helpful as it allows her to work carefully and checking her work.

Bob doesn't have a disability, but he was just dumped by his long term girlfriend yesterday and as a result barely slept last night. Because of his acute depression (a natural emotion that happens to all people sometimes), Bob has trouble focusing during the exam and his mind regularly drifts to ruminate on his personal issues. He knows the material well, but just can't stay on the task at hand. He runs at out of time before even attempting all the problems.

Now, I can imagine two situations.

1. For this particular exam, there really isn't a need to evaluate whether the students can quickly recall and apply the material. In this situation, what reason is there to not also give Bob an extra 30 minutes, same as Alice?

2. For whatever reason, part of the evaluation criteria for this exam is that the test taker is able to quickly recall and apply the material. To achieve a high score, being able to recall all the material is insufficient, it must be done quickly. In this case, basically Alice and Bob took different tests that measured different things.