Why do exams have time limits?

Why do exams, tests, quizzes etc. have time-limits placed on them? Is there any point, benefit, or reason to the time-limits? I honestly see no reason why they’re necessary.

You’re losing points you could potentially be earning, not because you didn’t comprehend the topic, or even answered incorrectly…but JUST because you weren’t quick enough. Are students being graded on their speed…or they’re actual comprehension of the subject(s)?

A common reason I hear is that “because its fair to everyone else, that they all receive the same mount of time to finish” but it seems like, by even including the time-limit in the first place, you’re creating sense of “fairness” that shouldn’t or doesn’t exist. Say, someone generally takes more time to finish things, they aren’t as quick as everyone else, it isn’t fair to them that they should be interrupted or rushed.
And if the time-limit is placed to prevent cheating…say, you’ve used up more time than other students, that doesn’t automatically suggest that you’re going to cheat, even if you’re the only one left in the testing area, the teacher(s) will still be monitoring you regardless. You could have cheated at any point during the test if you were going to, and if you did decide to cheat, you would’ve already been done well before the end of the time-limit placed.

Also, if the time-limit is created to see if the students are knowledgeable on a topic…taking up a lot of time doesn’t suggest the student doesn’t know the answers and isn’t knowledgeable on the topic.