You might not understand because 1) you are light (so not much resistance to lift) 2) you are fairly strong for your size 3) you have been emphasizing body weight exercises quite a bit.
So for you doing a pull up with no added weight might feel as easy as doing a push-up for most people. But the reality is that most "average" people have a hard time doing 3-5 reps on the strict pull-up with no added weight. Heck, I've seen plenty of guy with decent muscle mass who can't do more than 2 decent pull-ups.
Now. if you can only do pull-ups for 2 reps it's kinda like saying that the lightest you can go on the squat, even for your warm-ups, is 95% oif your max.
ON BODYWEIGHT EXERCISES YOU CANNOT LOWER THE WEIGTH. If you are shooting for 6 reps on the bench press, use 225lbs and only get 3, then you can always go down to 205 or 195 to get the 6. But what do you do on pull-ups if you can only get 3 reps with no added weight?
Sure you can use resistance bands, and I do from time to time, but it is not precise.
It's not the nature of the exercise (bodyweight) that makes it unsuitable as a strength movement if you are not already good at them, it's the fact that you cannot go lighter than your body weight.
So pull-ups should only be trained for strength if you are already good at them.
I would say the same thing with squats: training squats for strength is dumb if you can't squat properly.