Novellas are a great way to gain experience in writing. But there is so much more to it than that.
When it comes to online retailers like Amazon, there is no prejudice concerning novellas and their being less important than novels.
The algorithm follows what people like, so actually there may be no good reason not to write a novella.
Writing short fiction can help hone creative skills and build self-confidence before trying your hand at a longer, more complex piece of work.
As for traditional publishers, not many will be 100% keen about the prospect of having novellas submitted to them. Certainly some are, and most I think wouldn't mind as few bother to mention anything about novellas on their submissions page.
And agents and industry influencers know that the next popular thing could come from anywhere - they know it could very well be a novella.
So, even if you are an experienced writer, writing short fiction will boost your confidence and get you experimenting with different genres and ideas, and you didn’t think about this but - - - it is a great way to test markets.
Novellas are also a great way to start a series of books, and even renovate an existing series you feel has dried out, or if your sales have plateaued.
And these are just some of the reasons you are writing a novella.