So yeah, i was wondering why there is only few novels with epub's?
Is it hard to convert or something else?

It's not difficult to create an epub, but there's no reason for the majority of writers on RRL to do so. RRL's online posting format allows for a high level of interaction between authors and readers, as well as easy and instant updates and edits.

When creating an epub, you are "finalizing" your writing into a format that readers will upload to their ereader; once it's there, you are no longer able to affect the writing. Unless your story is complete and edited, there's no real reason to do this. Many authors who choose to go through the effort of completing and editing a story will then self-publish on Amazon or another site rather than posting it free to RRL.

In conclusion, it's not hard, but it's still not worth the effort.

Exactly what Unice said.

I could compile my series into an epub easily with Scrivener.

However, I'm continuously updating and editing because I'm preparing to publish. Most serious authors aren't going to make their finalized work available for free, and the ones who do are still most likely going to go through Amazon--reviews, reach, promotion, and more growth for subsequent books in a series.

As for the authors who don't intend to publish--some of them may not know programs like Scrivener exists. Others might be concerned that distributing an epub would make it easier for someone else to claim their work. New artists and writers often struggle to find a happy medium between caution and actually growing their audience.

Oh, you don't need to buy a program like Scrivener to compile epubs. Free software such as Calibre can easily convert between formats such as DOCX, PDF, EPUB, MOBI, LIT, and pretty much anything that you could conceive of as a text format. Depending on your starting file format, there may be a some formatting issues, but it's plenty good enough to create free epubs.