Kobo does lots of unexplained things.
The format thing has been a problem for lots of people ever since they launched the new web site. Their search has never worked very well (going back to when they were Shortcovers) with a Google search almost always giving better results of Kobo's own site. They've been soliciting reviews since they quit using Goodreads reviews yet they are nowhere to be found on the site. Books that are kePub only even though other places have the ePub (Kobo says this is a publisher choice, yet some publishers have called BS on that). Continuing to sell large numbers of titles that they know have problems. All kinds of odd things that have gone on for years.