There could be several reasons. Sometimes, a publisher might have a change in its editorial focus. Maybe they want to target a different demographic or they have a new strategic plan that doesn't include epic fantasy. Another reason could be competition. If there are too many publishers already in the epic fantasy market, they might feel it's too saturated to be profitable. Additionally, if they have had some bad experiences with epic fantasy authors, such as missed deadlines or low - quality manuscripts, it could also lead to them no longer publishing in this genre.
Maybe it's not selling well enough. If the sales figures for epic fantasy novels are consistently low, the publisher might decide to focus on more profitable genres.