There is always a risk of getting asked an explanation if you tell someone "I'm not interested." "Why not?" is the natural reaction.
What I don't understand is why you classify this as a "risk." I can understand if you're doing this as an in-person confrontation, but just sending a text saying "sorry I'm not interested in you" (or something more politely worded) has no risk associated with it at all. They ask why, and you could just... y'know... explain yourself in a respectful way. Yeah, I get it, it's not your duty to give an explanation. You don't owe anything to the other person. You could choose to ignore them and move on with your life. But why? Why are people so afraid to be honest and upfront with others? Why is this so dreadful that you actually flatout stop talking to a person completely just to avoid it? Like come on people, it's not that damn hard to just tell someone the truth.
And maybe I'm just more sympathetic because I've been on both sides of this. I've had a girl who was interested in me but I wasn't interested back. And I flatout told her and told her why because I have some sense of respect for her and realize while I don't owe them an explanation, I should give one because that's the "morally correct" thing to do. Yeah, it was a mess, she was upset, but we're still friends and that's a lot nicer than if I just cut her out of my life completely.
On the other end of it, I've had a girl I was interested in flatout stop talking to me. Never responded to texts never responded to anything. It was awful. I felt like shit. I was constantly wondering what I did wrong because I have no idea why she just decided to never talk to me again. I had no closure and while it would've hurt to hear her say she wasn't interested, it would've at least helped because all ignoring me did was flood my mind with doubts. Was I too ugly? Did I smell like shit? Did I say something wrong? Did she not like how I acted? It leaves so much open and can really mess with someone's head to leave it on that note. Sure, I don't deserve an explanation but I would've felt a whole damn lot better about that situation if I had one.
It's not about getting the hint - I got the hint and I was hardly even upset about her not being interested in me. What got me was how incredibly self-conscious it made me not knowing why she lost interest. Again, I know not everything's going to work out with perfect answers to all my problems and I should deal with it better. But it doesn't change the fact that ending something like that leaves it on a really shitty note.
Now there are exceptions - talking to a girl for a day on tinder and never talking again happens like 80% of the time and it doesn't really bother either person because there wasn't much closeness to begin with. But when you start building a relationship or even have a relationship with someone and then cut them out like that I just think it's plain wrong.