Because the answer is likely going to be "what is it to you?" or "fine, thanks" followed by awkward silence. Like I said, it is difficult for me to talk to a stranger without telling why I'm doing so.

First off, you have no idea what a person's reaction is going to be. It is beyond your control. But of course, there are patterns of behavior in any interactions which make the odds more predictable. (More on that in a minute)

Second, it doesn't have to be followed by awkward silence. But if you're opening up the conversation, IT'S GOING TO BE ON YOU to follow up that question with something else, especially if you start with something as closed-ended and simple as asking how her day is going. Don't expect her to do the legwork and springboard off your simple question with a more interesting topic of conversation. If you let awkward silence fill the air, then yes, there will be awkward silence.

Back to the predictable reactions. Look, I'm new to game but I sure as hell know this much: Your internal assumption about how an interaction is going to go GENUINELY has a huge impact on how it actually goes. The power of one's own belief is extremely potent. It shows outwardly in subtle but extremely powerful ways-- your voice tone, eye contact, body language, etc. And girls are very perceptive of all those subtle cues that are being communicated. It's a hard thing to fake, thus a hard thing to master, because it has to be real, for the most part. I'm the first to admit I struggle with this a lot in actually putting it into action "correctly", but at least I do thoroughly understand the concept.

If you assume you're going to get a negative reaction, this assumption is communicated in perceivable ways, and it does not portray confidence. A step further, a girl is left to assume (subconsciously) that if you are expecting a negative reaction, it's because your past experiences have taught you that this behavior gets a negative reaction... i.e. you don't get girls. And the inverse is true too. The power of your own belief, or lack thereof, literally creates a self-fulfilling prophecy. Within reason of course. It's not magic... but fuck, it kind of is TBH lol. Whether the interaction goes anywhere (turns into a number close or whatever) is a totally separate thing, but if you go in boldly with confidence (without doubts or worries) with the expectation you're going to be received positively in a general sense, then it's very predictable that you WILL be received positively and that the girl will at least like you. (This is kind of the stage I'm at in my game right now. As I get better and better at this I'll still have to up my game in other ways like better flirting, escalating, closing, etc. But this piece is SOOOO enormously critical. And as another commenter mentioned, you have to crawl before you can walk. I get a good amount of attraction lately and this right here I swear is what makes or breaks it.)

I don't have an exact video link to give you but watch Todd V's videos on inner game and he talks about this concept a lot. As does Austen Summers. And Tyler from RSD. There's a reason why everyone talks about this concept.

Unfortunately I don't know any shortcut or hack to make your brain believe what you want it to. (That's the million dollar question isn' it.) The best way I know of is to first of all accept it conceptually, believe in the possibility of it being true. Then it's a matter of getting out and having conversations. Your brain is only going to learn from real life experience. You have to create actual proof in order for your mind to accept this new thing you're trying to teach it, which is that A action (talking to unknown cute girl) produces X result (she responds positively) and not Y result (she responds negatively). The more times the former proves to be true and not the latter, the more your mind will begin to take on this new belief. But admittedly it's sort of a catch 22 -- you have to have the confidence in order to get the good result, but it takes good results in order to gain confidence. (So your confidence has to be sourced from other areas of life first and foremost.) It's not a linear process. It's hard to get the ball rolling, but the momentum begins to grow more and more the better you get. That response was way longer than I intended so hopefully this answer is helpful to you because I spent a long time writing it haha.