Lets get technical about Joystick clicking.
TBH I also don't like to sprint using that joy click, BUT!
On the other hand having a button for sprint is quite important since, for example, many games have an animation going in and out of sprinting that way you can't shoot as soon as you stop sprinting , there's a small delay for balancing.
If it were using the analog 100% signal of the joystick, that can be problematic since you lose the tactile feedback of the edge of the joystick.
For example: If I want to walk forward, usually I would just go forward as fast as I can without sprinting since its more comfortable, it's always the same speed and I have tactile feedback that I am at the maximum analog signal, then when it comes time, I can then slow down from 100% analog to 0% with ease and precision (because I have now felt the edges of the joystick).
It is very comfortable to keep your finger at max since you won't be fighting the spring of the joystick to keep it at say 75%. (by keeping finger at 100% you don't have to worry about not pushing it forwards)
I cant stress how improtant tactile feedback is improtant for this situation!
On the other hand, guessing where the edge of my joystick without being able to see it with my eyes so I don't sprint, is a different problem altogether. I would have to completly guess the position of my joystick or go by trial and error.
guessing it will make me walk slower or faster each and every time since I can't know for sure how far away I am from 100%. (muscle memory for precision wouldn't work since your hand change positions while you use it, it would be unreliable on a wand-like controller.)
If I want to know how far away from the edge I am, I would have to use trial and error; push at max untill i feel the tactile feedback of the edge of the joystick, then tone it down untill my player stops sprinting.
These methods mean that other players will have a different walk speed from you, meaning that walking as a group will be chaotic (for the lack of a better word)
As an example to this problem, imagine if RocketLeague didn't have a boost button and was using the alalog joystick 100% signal... idk if I would be playing it. It would be way too unreliable, and sometimes I just want to tap the boost.
Some FPS games force you to stop sprinting to regain stamina, yet again varying your walk speed from your team mates and guessing where the sprint limit is.
Some might say: Who cares if i walk 5% slower than my team mate/opponent?
But why wouldn't you want to walk at the same speed?
Imagine if all cars had cruise control always active on the highway at the speed limit (far fetched but let me explain).
This way you will never have to keep moving your pedal forward and backward to ajust to the speed of the car in front of you.
A constant speed that you always know that it is constant makes for a button, from there, being able to go less than that constant speed in analog increments makes for a perfect button. There's no guessing needed.
If we need to get technical, the button below the joystick is probably the very popular and simple button used in almost any electronics. Easiest example is the middle mouse clicks or many mouse macro buttons.
They can register a signal if not pressed all the way, but that's a flaw of the button itself. It needs quite alot of force to click and tilting that joystick probably changes the way the force travels mechanically to it; maybe it gets stuck on something because of the joystick is hitting something, or maybe its position isn't in the center of the joystick making it easier to click from certain directions. I'm not sure, but those are probable causes.
If that's the case, it's a design flaw.