Even selling through a large broker like daz or rosity still requires self promotion and marketing if you expect to be successful. There's only so much advertising you're going to get from a broker, because at the end of the day you're just one name on their roster of hundreds. You have to build a brand for yourself and work on building a fan base outside of the site your content is being sold through and all of that takes time and persistence.

There are content artists who run their own site as well as sell through brokerages but usually they aren't working by themselves.

Then there's sites like hivewire who launched a new figure and a new store at the same time and are still running a few years later, so it is possible. It just depends how much time and effort you're willing/able to put into it.