Why study medicine and become a doctor while there are hundreds of thousands of doctors that are very good at what they are doing?
Why become a software engineer and make apps while there are apps with the same functionality exist already?
Why open up a Chinese bistro when there are many?
Why?
Because they can do it and they can still make money of it. That's why.
Good examples, and I am sure we can come up with many other good examples, basically in this world there're a lot of everything, but still people are coming up with new ideas, they are finding ways to do it better than others, more interesting...
The bottom line is that you need to try it in order to find out! Can someone do it or not, can someone make profit or not? We can discuss it, but if someone doesn't try he will never know! And for sure we have many examples of people who succeeded in their plans, and we have even more people who have failed! It's on us to try something, it's on us to come up with an idea, to develop that idea, to cover everything we can, and to work hard to make something great!