Here is something I was told by more than one published author: Not everyone is a short story writer or needs to be. Writing short stories is not a good way to prepare for novels because, except for some technical aspects (grammar, spelling, etc.) they are not alike. Anyone who actually writes both knows this is true.
Many novelists do not write short stories and have no inclination to start. Check out your favorite novelists and see if they have more than a few short stories out there. Some have none at all. They went straight to novel writing because that was both what they wanted to do and what they do well. Some people are born novelists. Some are born short story writers. Others can do both.
Learning to write a good short story will not automatically make you a good novelist. The story structure is not the same, though you can practice things like grammar, proper sentences and such. I know some people who have been told that their short stories are unfinished novels. They have not always found the story structure they need to tell a compelling short story.
But there are those who have trouble with novel-length work as well. They're stories can be compact and well-told, but not presenting the larger structure you find in a novel.
Both short stories and novels are good. Both are difficult to write well. You do not have to be good at both to be a successful writer, whether you take the indie or the traditional path.
I had written more than 30 novels (and sold a few to small press publishers) before I wrote short stories. I had no interest in them. My first short stories grew out of writing exercises like writing what looks like a good opening line to a story every day (The exercise came from a book called 'What If' and was an excellent way to look at the crucial opening words). I got tired of one line after a few months and decided to expand that to the first 100 words. Well maybe 200. Well -- look. Short story. Wow. I didn't think I could do that!
I love writing short stories, though not as much as I love the length and depth of novels. I write quite a few of both. I used to sell quite a few shorter pieces to ezines and small press companies. Now, like the novels, they've gone to indie publication, though I also do a Flash Fiction each week on my blog.
But what should you write?
Write what you want to write. If you don't like to write short stories -- and especially if you don't like to read them -- then don't torture yourself trying to create shorter works. It's not necessary that every writer becomes proficient in every form. Would you tell poets they have to learn to write novels in order to be able to write good poetry?
What is important is that you write the stories you want to tell and you learn to do so well. This means perfecting your craft. Some people say they write short stories to hone their storytelling techniques. You can do the same with novels, of course, even if they are longer. Short stories are not a short cut to novels. I'm not saying you can't learn how to do dialog better, or improve your sentence structure, etc., by writing short stories, though. Just realize you can do the same by writing something you want to write.
Don't let anyone tell you that you have to write short stories before you can write novels. Don't let them tell you that you can't sell a novel to a publisher before you have written and sold shorter works. Even though having sold them won't hurt, they don't prove you can sustain the work of writing a full novel. In the end, the work you present to a publisher has to sell itself, and no amount of published short stories will make a poor novel better.
Only write shorter works if you want to write them. Use them for practice if you want to do so. Don't write them because you think they're a necessary step on the way to writing novels. And don't write novels if they don't appeal to you. This works both ways!